diff --git a/src/refdb_fs.c b/src/refdb_fs.c
index 658bebb61..876e84588 100644
--- a/src/refdb_fs.c
+++ b/src/refdb_fs.c
@@ -15,6 +15,7 @@
 #include "refdb.h"
 #include "refdb_fs.h"
 #include "iterator.h"
+#include "sortedcache.h"
 
 #include <git2/tag.h>
 #include <git2/object.h>
@@ -53,243 +54,149 @@ typedef struct refdb_fs_backend {
 	git_repository *repo;
 	char *path;
 
-	git_refcache refcache;
+	git_sortedcache *refcache;
 	int peeling_mode;
 } refdb_fs_backend;
 
-static int reference_read(
-	git_buf *file_content,
-	time_t *mtime,
-	const char *repo_path,
-	const char *ref_name,
-	int *updated)
+static int packref_cmp(const void *a_, const void *b_)
 {
-	git_buf path = GIT_BUF_INIT;
-	int result;
-
-	assert(file_content && repo_path && ref_name);
-
-	/* Determine the full path of the file */
-	if (git_buf_joinpath(&path, repo_path, ref_name) < 0)
-		return -1;
-
-	result = git_futils_readbuffer_updated(file_content, path.ptr, mtime, NULL, updated);
-	git_buf_free(&path);
-
-	return result;
+	const struct packref *a = a_, *b = b_;
+	return strcmp(a->name, b->name);
 }
 
-static int packed_parse_oid(
-	struct packref **ref_out,
-	const char **buffer_out,
-	const char *buffer_end)
+static int packed_reload(refdb_fs_backend *backend)
 {
-	struct packref *ref = NULL;
+	int error;
+	git_buf packedrefs = GIT_BUF_INIT;
+	char *scan, *eof, *eol;
 
-	const char *buffer = *buffer_out;
-	const char *refname_begin, *refname_end;
-
-	size_t refname_len;
-	git_oid id;
-
-	refname_begin = (buffer + GIT_OID_HEXSZ + 1);
-	if (refname_begin >= buffer_end || refname_begin[-1] != ' ')
-		goto corrupt;
-
-	/* Is this a valid object id? */
-	if (git_oid_fromstr(&id, buffer) < 0)
-		goto corrupt;
-
-	refname_end = memchr(refname_begin, '\n', buffer_end - refname_begin);
-	if (refname_end == NULL)
-		refname_end = buffer_end;
-
-	if (refname_end[-1] == '\r')
-		refname_end--;
-
-	refname_len = refname_end - refname_begin;
-
-	ref = git__calloc(1, sizeof(struct packref) + refname_len + 1);
-	GITERR_CHECK_ALLOC(ref);
-
-	memcpy(ref->name, refname_begin, refname_len);
-	ref->name[refname_len] = 0;
-
-	git_oid_cpy(&ref->oid, &id);
-
-	*ref_out = ref;
-	*buffer_out = refname_end + 1;
-	return 0;
-
-corrupt:
-	git__free(ref);
-	giterr_set(GITERR_REFERENCE, "The packed references file is corrupted");
-	return -1;
-}
-
-static int packed_parse_peel(
-	struct packref *tag_ref,
-	const char **buffer_out,
-	const char *buffer_end)
-{
-	const char *buffer = *buffer_out + 1;
-
-	assert(buffer[-1] == '^');
-
-	/* Ensure it's not the first entry of the file */
-	if (tag_ref == NULL)
-		goto corrupt;
-
-	if (buffer + GIT_OID_HEXSZ > buffer_end)
-		goto corrupt;
-
-	/* Is this a valid object id? */
-	if (git_oid_fromstr(&tag_ref->peel, buffer) < 0)
-		goto corrupt;
-
-	buffer = buffer + GIT_OID_HEXSZ;
-	if (*buffer == '\r')
-		buffer++;
-
-	if (buffer != buffer_end) {
-		if (*buffer == '\n')
-			buffer++;
-		else
-			goto corrupt;
-	}
-
-	tag_ref->flags |= PACKREF_HAS_PEEL;
-	*buffer_out = buffer;
-	return 0;
-
-corrupt:
-	giterr_set(GITERR_REFERENCE, "The packed references file is corrupted");
-	return -1;
-}
-
-static int packed_load(refdb_fs_backend *backend)
-{
-	int result, updated;
-	git_buf packfile = GIT_BUF_INIT;
-	const char *buffer_start, *buffer_end;
-	git_refcache *ref_cache = &backend->refcache;
-
-	/* First we make sure we have allocated the hash table */
-	if (ref_cache->packfile == NULL) {
-		ref_cache->packfile = git_strmap_alloc();
-		GITERR_CHECK_ALLOC(ref_cache->packfile);
-	}
-
-	if (backend->path == NULL)
+	if (!backend->path)
 		return 0;
 
-	result = reference_read(&packfile, &ref_cache->packfile_time,
-		backend->path, GIT_PACKEDREFS_FILE, &updated);
+	error = git_sortedcache_lockandload(backend->refcache, &packedrefs);
 
 	/*
-	 * If we couldn't find the file, we need to clear the table and
-	 * return. On any other error, we return that error. If everything
-	 * went fine and the file wasn't updated, then there's nothing new
-	 * for us here, so just return. Anything else means we need to
-	 * refresh the packed refs.
+	 * If we can't find the packed-refs, clear table and return.
+	 * Any other error just gets passed through.
+	 * If no error, and file wasn't changed, just return.
+	 * Anything else means we need to refresh the packed refs.
 	 */
-	if (result == GIT_ENOTFOUND) {
-		git_strmap_clear(ref_cache->packfile);
-		return 0;
+	if (error <= 0) {
+		if (error == GIT_ENOTFOUND) {
+			git_sortedcache_clear(backend->refcache, true);
+			giterr_clear();
+			error = 0;
+		}
+		return error;
 	}
 
-	if (result < 0)
-		return -1;
+	/* At this point, refresh the packed refs from the loaded buffer. */
 
-	if (!updated)
-		return 0;
+	git_sortedcache_clear(backend->refcache, false);
 
-	/*
-	 * At this point, we want to refresh the packed refs. We already
-	 * have the contents in our buffer.
-	 */
-	git_strmap_clear(ref_cache->packfile);
-
-	buffer_start = (const char *)packfile.ptr;
-	buffer_end = (const char *)(buffer_start) + packfile.size;
+	scan = (char *)packedrefs.ptr;
+	eof  = scan + packedrefs.size;
 
 	backend->peeling_mode = PEELING_NONE;
 
-	if (buffer_start[0] == '#') {
+	if (*scan == '#') {
 		static const char *traits_header = "# pack-refs with: ";
 
-		if (git__prefixcmp(buffer_start, traits_header) == 0) {
-			char *traits = (char *)buffer_start + strlen(traits_header);
-			char *traits_end = strchr(traits, '\n');
+		if (git__prefixcmp(scan, traits_header) == 0) {
+			scan += strlen(traits_header);
+			eol = strchr(scan, '\n');
 
-			if (traits_end == NULL)
+			if (!eol)
 				goto parse_failed;
+			*eol = '\0';
 
-			*traits_end = '\0';
-
-			if (strstr(traits, " fully-peeled ") != NULL) {
+			if (strstr(scan, " fully-peeled ") != NULL) {
 				backend->peeling_mode = PEELING_FULL;
-			} else if (strstr(traits, " peeled ") != NULL) {
+			} else if (strstr(scan, " peeled ") != NULL) {
 				backend->peeling_mode = PEELING_STANDARD;
 			}
 
-			buffer_start = traits_end + 1;
+			scan = eol + 1;
 		}
 	}
 
-	while (buffer_start < buffer_end && buffer_start[0] == '#') {
-		buffer_start = strchr(buffer_start, '\n');
-		if (buffer_start == NULL)
+	while (scan < eof && *scan == '#') {
+		if (!(eol = strchr(scan, '\n')))
 			goto parse_failed;
-
-		buffer_start++;
+		scan = eol + 1;
 	}
 
-	while (buffer_start < buffer_end) {
-		int err;
-		struct packref *ref = NULL;
+	while (scan < eof) {
+		struct packref *ref;
+		git_oid oid;
 
-		if (packed_parse_oid(&ref, &buffer_start, buffer_end) < 0)
+		/* parse "<OID> <refname>\n" */
+
+		if (git_oid_fromstr(&oid, scan) < 0)
 			goto parse_failed;
+		scan += GIT_OID_HEXSZ;
 
-		if (buffer_start[0] == '^') {
-			if (packed_parse_peel(ref, &buffer_start, buffer_end) < 0)
+		if (*scan++ != ' ')
+			goto parse_failed;
+		if (!(eol = strchr(scan, '\n')))
+			goto parse_failed;
+		*eol = '\0';
+		if (eol[-1] == '\r')
+			eol[-1] = '\0';
+
+		if (git_sortedcache_upsert((void **)&ref, backend->refcache, scan) < 0)
+			goto parse_failed;
+		scan = eol + 1;
+
+		git_oid_cpy(&ref->oid, &oid);
+
+		/* look for optional "^<OID>\n" */
+
+		if (*scan == '^') {
+			if (git_oid_fromstr(&oid, scan + 1) < 0)
 				goto parse_failed;
-		} else if (backend->peeling_mode == PEELING_FULL ||
-							(backend->peeling_mode == PEELING_STANDARD &&
-							git__prefixcmp(ref->name, GIT_REFS_TAGS_DIR) == 0)) {
-			ref->flags |= PACKREF_CANNOT_PEEL;
-		}
+			scan += GIT_OID_HEXSZ + 1;
 
-		git_strmap_insert(ref_cache->packfile, ref->name, ref, err);
-		if (err < 0)
-			goto parse_failed;
+			if (scan < eof) {
+				if (!(eol = strchr(scan, '\n')))
+					goto parse_failed;
+				scan = eol + 1;
+			}
+
+			git_oid_cpy(&ref->peel, &oid);
+			ref->flags |= PACKREF_HAS_PEEL;
+		}
+		else if (backend->peeling_mode == PEELING_FULL ||
+				(backend->peeling_mode == PEELING_STANDARD &&
+				 git__prefixcmp(ref->name, GIT_REFS_TAGS_DIR) == 0))
+			ref->flags |= PACKREF_CANNOT_PEEL;
 	}
 
-	git_buf_free(&packfile);
+	git_sortedcache_unlock(backend->refcache);
+	git_buf_free(&packedrefs);
+
 	return 0;
 
 parse_failed:
-	git_strmap_free(ref_cache->packfile);
-	ref_cache->packfile = NULL;
-	git_buf_free(&packfile);
+	giterr_set(GITERR_REFERENCE, "Corrupted packed references file");
+
+	git_sortedcache_clear(backend->refcache, false);
+	git_sortedcache_unlock(backend->refcache);
+	git_buf_free(&packedrefs);
+
 	return -1;
 }
 
-static int loose_parse_oid(git_oid *oid, const char *filename, git_buf *file_content)
+static int loose_parse_oid(
+	git_oid *oid, const char *filename, git_buf *file_content)
 {
-	size_t len;
-	const char *str;
+	const char *str = git_buf_cstr(file_content);
 
-	len = git_buf_len(file_content);
-	if (len < GIT_OID_HEXSZ)
+	if (git_buf_len(file_content) < GIT_OID_HEXSZ)
 		goto corrupted;
 
-	/* str is guranteed to be zero-terminated */
-	str = git_buf_cstr(file_content);
-
 	/* we need to get 40 OID characters from the file */
-	if (git_oid_fromstr(oid, git_buf_cstr(file_content)) < 0)
+	if (git_oid_fromstr(oid, str) < 0)
 		goto corrupted;
 
 	/* If the file is longer than 40 chars, the 41st must be a space */
@@ -302,77 +209,71 @@ corrupted:
 	return -1;
 }
 
-static int loose_lookup_to_packfile(
-	struct packref **ref_out,
-	refdb_fs_backend *backend,
-	const char *name)
+static int loose_readbuffer(git_buf *buf, const char *base, const char *path)
 {
-	git_buf ref_file = GIT_BUF_INIT;
-	struct packref *ref = NULL;
-	size_t name_len;
+	int error;
 
-	*ref_out = NULL;
+	/* build full path to file */
+	if ((error = git_buf_joinpath(buf, base, path)) < 0 ||
+		(error = git_futils_readbuffer(buf, buf->ptr)) < 0)
+		git_buf_free(buf);
 
-	if (reference_read(&ref_file, NULL, backend->path, name, NULL) < 0)
-		return -1;
-
-	/* skip symbolic refs */
-	if (!git__prefixcmp(git_buf_cstr(&ref_file), GIT_SYMREF)) {
-		git_buf_free(&ref_file);
-		return 0;
-	}
-
-	git_buf_rtrim(&ref_file);
-
-	name_len = strlen(name);
-	ref = git__calloc(1, sizeof(struct packref) + name_len + 1);
-	GITERR_CHECK_ALLOC(ref);
-
-	memcpy(ref->name, name, name_len);
-	ref->name[name_len] = 0;
-
-	if (loose_parse_oid(&ref->oid, name, &ref_file) < 0) {
-		git_buf_free(&ref_file);
-		git__free(ref);
-		return -1;
-	}
-
-	ref->flags = PACKREF_WAS_LOOSE;
-
-	*ref_out = ref;
-	git_buf_free(&ref_file);
-	return 0;
+	return error;
 }
 
+static int loose_lookup_to_packfile(refdb_fs_backend *backend, const char *name)
+{
+	int error = 0;
+	git_buf ref_file = GIT_BUF_INIT;
+	struct packref *ref = NULL;
+	git_oid oid;
+
+	/* if we fail to load the loose reference, assume someone changed
+	 * the filesystem under us and skip it...
+	 */
+	if (loose_readbuffer(&ref_file, backend->path, name) < 0) {
+		giterr_clear();
+		goto done;
+	}
+
+	/* skip symbolic refs */
+	if (!git__prefixcmp(git_buf_cstr(&ref_file), GIT_SYMREF))
+		goto done;
+
+	/* parse OID from file */
+	if ((error = loose_parse_oid(&oid, name, &ref_file)) < 0)
+		goto done;
+
+	git_sortedcache_lock(backend->refcache);
+
+	if (!(error = git_sortedcache_upsert(
+			(void **)&ref, backend->refcache, name))) {
+
+		git_oid_cpy(&ref->oid, &oid);
+		ref->flags = PACKREF_WAS_LOOSE;
+	}
+
+	git_sortedcache_unlock(backend->refcache);
+
+done:
+	git_buf_free(&ref_file);
+	return error;
+}
 
 static int _dirent_loose_load(void *data, git_buf *full_path)
 {
 	refdb_fs_backend *backend = (refdb_fs_backend *)data;
-	void *old_ref = NULL;
-	struct packref *ref;
 	const char *file_path;
-	int err;
 
-	if (git_path_isdir(full_path->ptr) == true)
+	if (git__suffixcmp(full_path->ptr, ".lock") == 0)
+		return 0;
+
+	if (git_path_isdir(full_path->ptr))
 		return git_path_direach(full_path, _dirent_loose_load, backend);
 
 	file_path = full_path->ptr + strlen(backend->path);
 
-	if (loose_lookup_to_packfile(&ref, backend, file_path) < 0)
-		return -1;
-
-	if (!ref)
-		return 0;
-
-	git_strmap_insert2(
-		backend->refcache.packfile, ref->name, ref, old_ref, err);
-	if (err < 0) {
-		git__free(ref);
-		return -1;
-	}
-
-	git__free(old_ref);
-	return 0;
+	return loose_lookup_to_packfile(backend, file_path);
 }
 
 /*
@@ -383,11 +284,8 @@ static int _dirent_loose_load(void *data, git_buf *full_path)
  */
 static int packed_loadloose(refdb_fs_backend *backend)
 {
+	int error;
 	git_buf refs_path = GIT_BUF_INIT;
-	int result;
-
-	/* the packfile must have been previously loaded! */
-	assert(backend->refcache.packfile);
 
 	if (git_buf_joinpath(&refs_path, backend->path, GIT_REFS_DIR) < 0)
 		return -1;
@@ -397,10 +295,11 @@ static int packed_loadloose(refdb_fs_backend *backend)
 	 * This will overwrite any old packed entries with their
 	 * updated loose versions
 	 */
-	result = git_path_direach(&refs_path, _dirent_loose_load, backend);
+	error = git_path_direach(&refs_path, _dirent_loose_load, backend);
+
 	git_buf_free(&refs_path);
 
-	return result;
+	return error;
 }
 
 static int refdb_fs_backend__exists(
@@ -408,23 +307,17 @@ static int refdb_fs_backend__exists(
 	git_refdb_backend *_backend,
 	const char *ref_name)
 {
-	refdb_fs_backend *backend;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 	git_buf ref_path = GIT_BUF_INIT;
 
-	assert(_backend);
-	backend = (refdb_fs_backend *)_backend;
+	assert(backend);
 
-	if (packed_load(backend) < 0)
+	if (packed_reload(backend) < 0 ||
+		git_buf_joinpath(&ref_path, backend->path, ref_name) < 0)
 		return -1;
 
-	if (git_buf_joinpath(&ref_path, backend->path, ref_name) < 0)
-		return -1;
-
-	if (git_path_isfile(ref_path.ptr) == true ||
-		git_strmap_exists(backend->refcache.packfile, ref_path.ptr))
-		*exists = 1;
-	else
-		*exists = 0;
+	*exists = git_path_isfile(ref_path.ptr) ||
+		git_sortedcache_lookup(backend->refcache, ref_name);
 
 	git_buf_free(&ref_path);
 	return 0;
@@ -456,69 +349,39 @@ static int loose_lookup(
 	refdb_fs_backend *backend,
 	const char *ref_name)
 {
-	const char *target;
-	git_oid oid;
 	git_buf ref_file = GIT_BUF_INIT;
 	int error = 0;
 
 	if (out)
 		*out = NULL;
 
-	error = reference_read(&ref_file, NULL, backend->path, ref_name, NULL);
+	if ((error = loose_readbuffer(&ref_file, backend->path, ref_name)) < 0)
+		/* cannot read loose ref file - gah */;
+	else if (git__prefixcmp(git_buf_cstr(&ref_file), GIT_SYMREF) == 0) {
+		const char *target;
 
-	if (error < 0)
-		goto done;
-
-	if (git__prefixcmp(git_buf_cstr(&ref_file), GIT_SYMREF) == 0) {
 		git_buf_rtrim(&ref_file);
 
-		if ((target = loose_parse_symbolic(&ref_file)) == NULL) {
+		if (!(target = loose_parse_symbolic(&ref_file)))
 			error = -1;
-			goto done;
-		}
-
-		if (out)
+		else if (out != NULL)
 			*out = git_reference__alloc_symbolic(ref_name, target);
 	} else {
-		if ((error = loose_parse_oid(&oid, ref_name, &ref_file)) < 0)
-			goto done;
+		git_oid oid;
 
-		if (out)
+		if (!(error = loose_parse_oid(&oid, ref_name, &ref_file)) &&
+			out != NULL)
 			*out = git_reference__alloc(ref_name, &oid, NULL);
 	}
 
-	if (out && *out == NULL)
-		error = -1;
-
-done:
 	git_buf_free(&ref_file);
 	return error;
 }
 
-static int packed_map_entry(
-	struct packref **entry,
-	khiter_t *pos,
-	refdb_fs_backend *backend,
-	const char *ref_name)
+static int ref_error_notfound(const char *name)
 {
-	git_strmap *packfile_refs;
-
-	if (packed_load(backend) < 0)
-		return -1;
-
-	/* Look up on the packfile */
-	packfile_refs = backend->refcache.packfile;
-
-	*pos = git_strmap_lookup_index(packfile_refs, ref_name);
-
-	if (!git_strmap_valid_index(packfile_refs, *pos)) {
-		giterr_set(GITERR_REFERENCE, "Reference '%s' not found", ref_name);
-		return GIT_ENOTFOUND;
-	}
-
-	*entry = git_strmap_value_at(packfile_refs, *pos);
-
-	return 0;
+	giterr_set(GITERR_REFERENCE, "Reference '%s' not found", name);
+	return GIT_ENOTFOUND;
 }
 
 static int packed_lookup(
@@ -526,18 +389,25 @@ static int packed_lookup(
 	refdb_fs_backend *backend,
 	const char *ref_name)
 {
-	struct packref *entry;
-	khiter_t pos;
 	int error = 0;
+	struct packref *entry;
 
-	if ((error = packed_map_entry(&entry, &pos, backend, ref_name)) < 0)
-		return error;
-
-	if ((*out = git_reference__alloc(ref_name,
-		&entry->oid, &entry->peel)) == NULL)
+	if (packed_reload(backend) < 0)
 		return -1;
 
-	return 0;
+	git_sortedcache_lock(backend->refcache);
+
+	entry = git_sortedcache_lookup(backend->refcache, ref_name);
+	if (!entry) {
+		error = ref_error_notfound(ref_name);
+	} else {
+		*out = git_reference__alloc(ref_name, &entry->oid, &entry->peel);
+		if (!*out)
+			error = -1;
+	}
+
+	git_sortedcache_unlock(backend->refcache);
+	return error;
 }
 
 static int refdb_fs_backend__lookup(
@@ -545,24 +415,22 @@ static int refdb_fs_backend__lookup(
 	git_refdb_backend *_backend,
 	const char *ref_name)
 {
-	refdb_fs_backend *backend;
-	int result;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
+	int error;
 
-	assert(_backend);
+	assert(backend);
 
-	backend = (refdb_fs_backend *)_backend;
-
-	if ((result = loose_lookup(out, backend, ref_name)) == 0)
+	if (!(error = loose_lookup(out, backend, ref_name)))
 		return 0;
 
 	/* only try to lookup this reference on the packfile if it
 	 * wasn't found on the loose refs; not if there was a critical error */
-	if (result == GIT_ENOTFOUND) {
+	if (error == GIT_ENOTFOUND) {
 		giterr_clear();
-		result = packed_lookup(out, backend, ref_name);
+		error = packed_lookup(out, backend, ref_name);
 	}
 
-	return result;
+	return error;
 }
 
 typedef struct {
@@ -573,8 +441,8 @@ typedef struct {
 	git_pool pool;
 	git_vector loose;
 
-	unsigned int loose_pos;
-	khiter_t packed_pos;
+	size_t loose_pos;
+	size_t packed_pos;
 } refdb_fs_iter;
 
 static void refdb_fs_backend__iterator_free(git_reference_iterator *_iter)
@@ -589,7 +457,6 @@ static void refdb_fs_backend__iterator_free(git_reference_iterator *_iter)
 static int iter_load_loose_paths(refdb_fs_backend *backend, refdb_fs_iter *iter)
 {
 	int error = 0;
-	git_strmap *packfile = backend->refcache.packfile;
 	git_buf path = GIT_BUF_INIT;
 	git_iterator *fsit = NULL;
 	const git_index_entry *entry = NULL;
@@ -597,18 +464,18 @@ static int iter_load_loose_paths(refdb_fs_backend *backend, refdb_fs_iter *iter)
 	if (!backend->path) /* do nothing if no path for loose refs */
 		return 0;
 
-	if (git_buf_printf(&path, "%s/refs", backend->path) < 0)
-		return -1;
+	if ((error = git_buf_printf(&path, "%s/refs", backend->path)) < 0 ||
+		(error = git_iterator_for_filesystem(
+			&fsit, git_buf_cstr(&path), 0, NULL, NULL)) < 0) {
+		git_buf_free(&path);
+		return error;
+	}
 
-	if ((error = git_iterator_for_filesystem(
-			&fsit, git_buf_cstr(&path), 0, NULL, NULL)) < 0 ||
-		(error = git_vector_init(&iter->loose, 8, NULL)) < 0 ||
-		(error = git_buf_sets(&path, GIT_REFS_DIR)) < 0)
-		goto cleanup;
+	error = git_buf_sets(&path, GIT_REFS_DIR);
 
-	while (!git_iterator_advance(&entry, fsit)) {
+	while (!error && !git_iterator_advance(&entry, fsit)) {
 		const char *ref_name;
-		khiter_t pos;
+		struct packref *ref;
 		char *ref_dup;
 
 		git_buf_truncate(&path, strlen(GIT_REFS_DIR));
@@ -619,26 +486,23 @@ static int iter_load_loose_paths(refdb_fs_backend *backend, refdb_fs_iter *iter)
 			(iter->glob && p_fnmatch(iter->glob, ref_name, 0) != 0))
 			continue;
 
-		pos = git_strmap_lookup_index(packfile, ref_name);
-		if (git_strmap_valid_index(packfile, pos)) {
-			struct packref *ref = git_strmap_value_at(packfile, pos);
+		git_sortedcache_lock(backend->refcache);
+		ref = git_sortedcache_lookup(backend->refcache, ref_name);
+		if (ref)
 			ref->flags |= PACKREF_SHADOWED;
-		}
+		git_sortedcache_unlock(backend->refcache);
 
-		if (!(ref_dup = git_pool_strdup(&iter->pool, ref_name))) {
+		ref_dup = git_pool_strdup(&iter->pool, ref_name);
+		if (!ref_dup)
 			error = -1;
-			goto cleanup;
-		}
-
-		if ((error = git_vector_insert(&iter->loose, ref_dup)) < 0)
-			goto cleanup;
+		else
+			error = git_vector_insert(&iter->loose, ref_dup);
 	}
 
-cleanup:
 	git_iterator_free(fsit);
 	git_buf_free(&path);
 
-	return 0;
+	return error;
 }
 
 static int refdb_fs_backend__iterator_next(
@@ -646,7 +510,7 @@ static int refdb_fs_backend__iterator_next(
 {
 	refdb_fs_iter *iter = (refdb_fs_iter *)_iter;
 	refdb_fs_backend *backend = (refdb_fs_backend *)iter->parent.db->backend;
-	git_strmap *packfile = backend->refcache.packfile;
+	struct packref *ref;
 
 	while (iter->loose_pos < iter->loose.length) {
 		const char *path = git_vector_get(&iter->loose, iter->loose_pos++);
@@ -657,17 +521,12 @@ static int refdb_fs_backend__iterator_next(
 		giterr_clear();
 	}
 
-	while (iter->packed_pos < kh_end(packfile)) {
-		struct packref *ref = NULL;
+	git_sortedcache_lock(backend->refcache);
 
-		while (!kh_exist(packfile, iter->packed_pos)) {
-			iter->packed_pos++;
-			if (iter->packed_pos == kh_end(packfile))
-				return GIT_ITEROVER;
-		}
-
-		ref = kh_val(packfile, iter->packed_pos);
-		iter->packed_pos++;
+	while (iter->packed_pos < git_sortedcache_entrycount(backend->refcache)) {
+		ref = git_sortedcache_entry(backend->refcache, iter->packed_pos++);
+		if (!ref) /* stop now if another thread deleted refs and we past end */
+			break;
 
 		if (ref->flags & PACKREF_SHADOWED)
 			continue;
@@ -676,12 +535,11 @@ static int refdb_fs_backend__iterator_next(
 			continue;
 
 		*out = git_reference__alloc(ref->name, &ref->oid, &ref->peel);
-		if (*out == NULL)
-			return -1;
-
-		return 0;
+		git_sortedcache_unlock(backend->refcache);
+		return (*out != NULL) ? 0 : -1;
 	}
 
+	git_sortedcache_unlock(backend->refcache);
 	return GIT_ITEROVER;
 }
 
@@ -690,14 +548,10 @@ static int refdb_fs_backend__iterator_next_name(
 {
 	refdb_fs_iter *iter = (refdb_fs_iter *)_iter;
 	refdb_fs_backend *backend = (refdb_fs_backend *)iter->parent.db->backend;
-	git_strmap *packfile = backend->refcache.packfile;
 
 	while (iter->loose_pos < iter->loose.length) {
 		const char *path = git_vector_get(&iter->loose, iter->loose_pos++);
 
-		if (git_strmap_exists(packfile, path))
-			continue;
-
 		if (loose_lookup(NULL, backend, path) != 0) {
 			giterr_clear();
 			continue;
@@ -707,22 +561,25 @@ static int refdb_fs_backend__iterator_next_name(
 		return 0;
 	}
 
-	while (iter->packed_pos < kh_end(packfile)) {
-		while (!kh_exist(packfile, iter->packed_pos)) {
-			iter->packed_pos++;
-			if (iter->packed_pos == kh_end(packfile))
-				return GIT_ITEROVER;
-		}
+	git_sortedcache_lock(backend->refcache);
 
-		*out = kh_key(packfile, iter->packed_pos);
-		iter->packed_pos++;
+	while (iter->packed_pos < git_sortedcache_entrycount(backend->refcache)) {
+		struct packref *ref =
+			git_sortedcache_entry(backend->refcache, iter->packed_pos++);
+
+		if (ref->flags & PACKREF_SHADOWED)
+			continue;
+
+		*out = ref->name;
 
 		if (iter->glob && p_fnmatch(iter->glob, *out, 0) != 0)
 			continue;
 
+		git_sortedcache_unlock(backend->refcache);
 		return 0;
 	}
 
+	git_sortedcache_unlock(backend->refcache);
 	return GIT_ITEROVER;
 }
 
@@ -730,18 +587,18 @@ static int refdb_fs_backend__iterator(
 	git_reference_iterator **out, git_refdb_backend *_backend, const char *glob)
 {
 	refdb_fs_iter *iter;
-	refdb_fs_backend *backend;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 
-	assert(_backend);
-	backend = (refdb_fs_backend *)_backend;
+	assert(backend);
 
-	if (packed_load(backend) < 0)
+	if (packed_reload(backend) < 0)
 		return -1;
 
 	iter = git__calloc(1, sizeof(refdb_fs_iter));
 	GITERR_CHECK_ALLOC(iter);
 
-	if (git_pool_init(&iter->pool, 1, 0) < 0)
+	if (git_pool_init(&iter->pool, 1, 0) < 0 ||
+		git_vector_init(&iter->loose, 8, NULL) < 0)
 		goto fail;
 
 	if (glob != NULL &&
@@ -786,15 +643,16 @@ static int reference_path_available(
 	const char* old_ref,
 	int force)
 {
-	struct packref *this_ref;
+	size_t i;
 
-	if (packed_load(backend) < 0)
+	if (packed_reload(backend) < 0)
 		return -1;
 
 	if (!force) {
 		int exists;
 
-		if (refdb_fs_backend__exists(&exists, (git_refdb_backend *)backend, new_ref) < 0)
+		if (refdb_fs_backend__exists(
+				&exists, (git_refdb_backend *)backend, new_ref) < 0)
 			return -1;
 
 		if (exists) {
@@ -805,14 +663,21 @@ static int reference_path_available(
 		}
 	}
 
-	git_strmap_foreach_value(backend->refcache.packfile, this_ref, {
+	git_sortedcache_lock(backend->refcache);
+
+	for (i = 0; i < git_sortedcache_entrycount(backend->refcache); ++i) {
+		struct packref *this_ref =
+			git_sortedcache_entry(backend->refcache, i);
+
 		if (!ref_is_available(old_ref, new_ref, this_ref->name)) {
+			git_sortedcache_unlock(backend->refcache);
 			giterr_set(GITERR_REFERENCE,
 				"The path to reference '%s' collides with an existing one", new_ref);
 			return -1;
 		}
-	});
+	}
 
+	git_sortedcache_unlock(backend->refcache);
 	return 0;
 }
 
@@ -839,12 +704,9 @@ static int loose_write(refdb_fs_backend *backend, const git_reference *ref)
 
 	if (ref->type == GIT_REF_OID) {
 		char oid[GIT_OID_HEXSZ + 1];
-
-		git_oid_fmt(oid, &ref->target.oid);
-		oid[GIT_OID_HEXSZ] = '\0';
+		git_oid_nfmt(oid, sizeof(oid), &ref->target.oid);
 
 		git_filebuf_printf(&file, "%s\n", oid);
-
 	} else if (ref->type == GIT_REF_SYMBOLIC) {
 		git_filebuf_printf(&file, GIT_SYMREF "%s\n", ref->target.symbolic);
 	} else {
@@ -854,14 +716,6 @@ static int loose_write(refdb_fs_backend *backend, const git_reference *ref)
 	return git_filebuf_commit(&file, GIT_REFS_FILE_MODE);
 }
 
-static int packed_sort(const void *a, const void *b)
-{
-	const struct packref *ref_a = (const struct packref *)a;
-	const struct packref *ref_b = (const struct packref *)b;
-
-	return strcmp(ref_a->name, ref_b->name);
-}
-
 /*
  * Find out what object this reference resolves to.
  *
@@ -914,9 +768,7 @@ static int packed_find_peel(refdb_fs_backend *backend, struct packref *ref)
 static int packed_write_ref(struct packref *ref, git_filebuf *file)
 {
 	char oid[GIT_OID_HEXSZ + 1];
-
-	git_oid_fmt(oid, &ref->oid);
-	oid[GIT_OID_HEXSZ] = 0;
+	git_oid_nfmt(oid, sizeof(oid), &ref->oid);
 
 	/*
 	 * For references that peel to an object in the repo, we must
@@ -930,8 +782,7 @@ static int packed_write_ref(struct packref *ref, git_filebuf *file)
 	 */
 	if (ref->flags & PACKREF_HAS_PEEL) {
 		char peel[GIT_OID_HEXSZ + 1];
-		git_oid_fmt(peel, &ref->peel);
-		peel[GIT_OID_HEXSZ] = 0;
+		git_oid_nfmt(peel, sizeof(peel), &ref->peel);
 
 		if (git_filebuf_printf(file, "%s %s\n^%s\n", oid, ref->name, peel) < 0)
 			return -1;
@@ -954,16 +805,16 @@ static int packed_write_ref(struct packref *ref, git_filebuf *file)
  * is well-written, because we are destructing references
  * here otherwise.
  */
-static int packed_remove_loose(
-	refdb_fs_backend *backend,
-	git_vector *packing_list)
+static int packed_remove_loose(refdb_fs_backend *backend)
 {
 	size_t i;
 	git_buf full_path = GIT_BUF_INIT;
 	int failed = 0;
 
-	for (i = 0; i < packing_list->length; ++i) {
-		struct packref *ref = git_vector_get(packing_list, i);
+	/* backend->refcache is already locked when this is called */
+
+	for (i = 0; i < git_sortedcache_entrycount(backend->refcache); ++i) {
+		struct packref *ref = git_sortedcache_entry(backend->refcache, i);
 
 		if ((ref->flags & PACKREF_WAS_LOOSE) == 0)
 			continue;
@@ -971,14 +822,13 @@ static int packed_remove_loose(
 		if (git_buf_joinpath(&full_path, backend->path, ref->name) < 0)
 			return -1; /* critical; do not try to recover on oom */
 
-		if (git_path_exists(full_path.ptr) == true && p_unlink(full_path.ptr) < 0) {
+		if (git_path_exists(full_path.ptr) && p_unlink(full_path.ptr) < 0) {
 			if (failed)
 				continue;
 
 			giterr_set(GITERR_REFERENCE,
 				"Failed to remove loose reference '%s' after packing: %s",
 				full_path.ptr, strerror(errno));
-
 			failed = 1;
 		}
 
@@ -1002,33 +852,14 @@ static int packed_write(refdb_fs_backend *backend)
 	git_filebuf pack_file = GIT_FILEBUF_INIT;
 	size_t i;
 	git_buf pack_file_path = GIT_BUF_INIT;
-	git_vector packing_list;
-	unsigned int total_refs;
 
-	assert(backend && backend->refcache.packfile);
-
-	total_refs =
-		(unsigned int)git_strmap_num_entries(backend->refcache.packfile);
-
-	if (git_vector_init(&packing_list, total_refs, packed_sort) < 0)
+	/* lock the cache to updates while we do this */
+	if (git_sortedcache_lock(backend->refcache) < 0)
 		return -1;
 
-	/* Load all the packfile into a vector */
-	{
-		struct packref *reference;
-
-		/* cannot fail: vector already has the right size */
-		git_strmap_foreach_value(backend->refcache.packfile, reference, {
-			git_vector_insert(&packing_list, reference);
-		});
-	}
-
-	/* sort the vector so the entries appear sorted on the packfile */
-	git_vector_sort(&packing_list);
-
-	/* Now we can open the file! */
-	if (git_buf_joinpath(&pack_file_path,
-		backend->path, GIT_PACKEDREFS_FILE) < 0)
+	/* Open the file! */
+	if (git_buf_joinpath(
+			&pack_file_path, backend->path, GIT_PACKEDREFS_FILE) < 0)
 		goto cleanup_memory;
 
 	if (git_filebuf_open(&pack_file, pack_file_path.ptr, 0) < 0)
@@ -1040,8 +871,9 @@ static int packed_write(refdb_fs_backend *backend)
 	if (git_filebuf_printf(&pack_file, "%s\n", GIT_PACKEDREFS_HEADER) < 0)
 		goto cleanup_packfile;
 
-	for (i = 0; i < packing_list.length; ++i) {
-		struct packref *ref = (struct packref *)git_vector_get(&packing_list, i);
+	for (i = 0; i < git_sortedcache_entrycount(backend->refcache); ++i) {
+		struct packref *ref =
+			git_sortedcache_entry(backend->refcache, i);
 
 		if (packed_find_peel(backend, ref) < 0)
 			goto cleanup_packfile;
@@ -1057,16 +889,16 @@ static int packed_write(refdb_fs_backend *backend)
 
 	/* when and only when the packfile has been properly written,
 	 * we can go ahead and remove the loose refs */
-	 if (packed_remove_loose(backend, &packing_list) < 0)
-		 goto cleanup_memory;
+	if (packed_remove_loose(backend) < 0)
+		goto cleanup_memory;
 
-	 {
-		struct stat st;
-		if (p_stat(pack_file_path.ptr, &st) == 0)
-			backend->refcache.packfile_time = st.st_mtime;
-	 }
+	git_sortedcache_unlock(backend->refcache);
+
+	 /* update filestamp to latest value */
+	if (git_futils_filestamp_check(
+			&backend->refcache->stamp, pack_file_path.ptr) < 0)
+		giterr_clear();
 
-	git_vector_free(&packing_list);
 	git_buf_free(&pack_file_path);
 
 	/* we're good now */
@@ -1076,7 +908,7 @@ cleanup_packfile:
 	git_filebuf_cleanup(&pack_file);
 
 cleanup_memory:
-	git_vector_free(&packing_list);
+	git_sortedcache_unlock(backend->refcache);
 	git_buf_free(&pack_file_path);
 
 	return -1;
@@ -1087,11 +919,10 @@ static int refdb_fs_backend__write(
 	const git_reference *ref,
 	int force)
 {
-	refdb_fs_backend *backend;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 	int error;
 
-	assert(_backend);
-	backend = (refdb_fs_backend *)_backend;
+	assert(backend);
 
 	error = reference_path_available(backend, ref->name, NULL, force);
 	if (error < 0)
@@ -1104,17 +935,13 @@ static int refdb_fs_backend__delete(
 	git_refdb_backend *_backend,
 	const char *ref_name)
 {
-	refdb_fs_backend *backend;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 	git_buf loose_path = GIT_BUF_INIT;
-	struct packref *pack_ref;
-	khiter_t pack_ref_pos;
+	size_t pack_pos;
 	int error = 0;
 	bool loose_deleted = 0;
 
-	assert(_backend);
-	assert(ref_name);
-
-	backend = (refdb_fs_backend *)_backend;
+	assert(backend && ref_name);
 
 	/* If a loose reference exists, remove it from the filesystem */
 	if (git_buf_joinpath(&loose_path, backend->path, ref_name) < 0)
@@ -1130,19 +957,23 @@ static int refdb_fs_backend__delete(
 	if (error != 0)
 		return error;
 
+	if (packed_reload(backend) < 0)
+		return -1;
+
 	/* If a packed reference exists, remove it from the packfile and repack */
-	error = packed_map_entry(&pack_ref, &pack_ref_pos, backend, ref_name);
+	if (git_sortedcache_lock(backend->refcache) < 0)
+		return -1;
+
+	if (!(error = git_sortedcache_lookup_index(
+			&pack_pos, backend->refcache, ref_name)))
+		error = git_sortedcache_remove(backend->refcache, pack_pos, false);
+
+	git_sortedcache_unlock(backend->refcache);
 
 	if (error == GIT_ENOTFOUND)
-		return loose_deleted ? 0 : GIT_ENOTFOUND;
+		return loose_deleted ? 0 : ref_error_notfound(ref_name);
 
-	if (error == 0) {
-		git_strmap_delete_at(backend->refcache.packfile, pack_ref_pos);
-		git__free(pack_ref);
-		error = packed_write(backend);
-	}
-
-	return error;
+	return packed_write(backend);
 }
 
 static int refdb_fs_backend__rename(
@@ -1152,53 +983,44 @@ static int refdb_fs_backend__rename(
 	const char *new_name,
 	int force)
 {
-	refdb_fs_backend *backend;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 	git_reference *old, *new;
 	int error;
 
-	assert(_backend);
-	backend = (refdb_fs_backend *)_backend;
+	assert(backend);
 
-	error = reference_path_available(backend, new_name, old_name, force);
-	if (error < 0)
+	if ((error = reference_path_available(
+			backend, new_name, old_name, force)) < 0 ||
+		(error = refdb_fs_backend__lookup(&old, _backend, old_name)) < 0)
 		return error;
 
-	error = refdb_fs_backend__lookup(&old, _backend, old_name);
-	if (error < 0)
-		return error;
-
-	error = refdb_fs_backend__delete(_backend, old_name);
-	if (error < 0) {
+	if ((error = refdb_fs_backend__delete(_backend, old_name)) < 0) {
 		git_reference_free(old);
 		return error;
 	}
 
-	new = realloc(old, sizeof(git_reference) + strlen(new_name) + 1);
-	memcpy(new->name, new_name, strlen(new_name) + 1);
+	new = git_reference__set_name(old, new_name);
+	if (!new) {
+		git_reference_free(old);
+		return -1;
+	}
 
-	error = loose_write(backend, new);
-	if (error < 0) {
+	if ((error = loose_write(backend, new)) < 0 || out == NULL) {
 		git_reference_free(new);
 		return error;
 	}
 
-	if (out) {
-		*out = new;
-	} else {
-		git_reference_free(new);
-	}
-
+	*out = new;
 	return 0;
 }
 
 static int refdb_fs_backend__compress(git_refdb_backend *_backend)
 {
-	refdb_fs_backend *backend;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 
-	assert(_backend);
-	backend = (refdb_fs_backend *)_backend;
+	assert(backend);
 
-	if (packed_load(backend) < 0 || /* load the existing packfile */
+	if (packed_reload(backend) < 0 || /* load the existing packfile */
 		packed_loadloose(backend) < 0 || /* add all the loose refs */
 		packed_write(backend) < 0) /* write back to disk */
 		return -1;
@@ -1206,29 +1028,13 @@ static int refdb_fs_backend__compress(git_refdb_backend *_backend)
 	return 0;
 }
 
-static void refcache_free(git_refcache *refs)
-{
-	assert(refs);
-
-	if (refs->packfile) {
-		struct packref *reference;
-
-		git_strmap_foreach_value(refs->packfile, reference, {
-			git__free(reference);
-		});
-
-		git_strmap_free(refs->packfile);
-	}
-}
-
 static void refdb_fs_backend__free(git_refdb_backend *_backend)
 {
-	refdb_fs_backend *backend;
+	refdb_fs_backend *backend = (refdb_fs_backend *)_backend;
 
-	assert(_backend);
-	backend = (refdb_fs_backend *)_backend;
+	assert(backend);
 
-	refcache_free(&backend->refcache);
+	git_sortedcache_free(backend->refcache);
 	git__free(backend->path);
 	git__free(backend);
 }
@@ -1252,7 +1058,7 @@ static int setup_namespace(git_buf *path, git_repository *repo)
 	if (parts == NULL)
 		return -1;
 
-	/**
+	/*
 	 * From `man gitnamespaces`:
 	 *  namespaces which include a / will expand to a hierarchy
 	 *  of namespaces; for example, GIT_NAMESPACE=foo/bar will store
@@ -1269,7 +1075,7 @@ static int setup_namespace(git_buf *path, git_repository *repo)
 	if (git_futils_mkdir_r(git_buf_cstr(path), repo->path_repository, 0777) < 0)
 		return -1;
 
-	/* Return the root of the namespaced path, i.e. without the trailing '/refs' */
+	/* Return root of the namespaced path, i.e. without the trailing '/refs' */
 	git_buf_rtruncate_at_char(path, '/');
 	return 0;
 }
@@ -1286,13 +1092,19 @@ int git_refdb_backend_fs(
 
 	backend->repo = repository;
 
-	if (setup_namespace(&path, repository) < 0) {
-		git__free(backend);
-		return -1;
-	}
+	if (setup_namespace(&path, repository) < 0)
+		goto fail;
 
 	backend->path = git_buf_detach(&path);
 
+	if (git_buf_joinpath(&path, backend->path, GIT_PACKEDREFS_FILE) < 0 ||
+		git_sortedcache_new(
+			&backend->refcache, offsetof(struct packref, name),
+			NULL, NULL, packref_cmp, git_buf_cstr(&path)) < 0)
+		goto fail;
+
+	git_buf_free(&path);
+
 	backend->parent.exists = &refdb_fs_backend__exists;
 	backend->parent.lookup = &refdb_fs_backend__lookup;
 	backend->parent.iterator = &refdb_fs_backend__iterator;
@@ -1304,4 +1116,10 @@ int git_refdb_backend_fs(
 
 	*backend_out = (git_refdb_backend *)backend;
 	return 0;
+
+fail:
+	git_buf_free(&path);
+	git__free(backend->path);
+	git__free(backend);
+	return -1;
 }
diff --git a/tests-clar/threads/refdb.c b/tests-clar/threads/refdb.c
new file mode 100644
index 000000000..11e90a458
--- /dev/null
+++ b/tests-clar/threads/refdb.c
@@ -0,0 +1,200 @@
+#include "clar_libgit2.h"
+#include "git2/refdb.h"
+#include "refdb.h"
+
+static git_repository *g_repo;
+static int g_expected = 0;
+
+void test_threads_refdb__initialize(void)
+{
+	g_repo = NULL;
+}
+
+void test_threads_refdb__cleanup(void)
+{
+	cl_git_sandbox_cleanup();
+	g_repo = NULL;
+}
+
+#define REPEAT 20
+#define THREADS 20
+
+static void *iterate_refs(void *arg)
+{
+	git_reference_iterator *i;
+	git_reference *ref;
+	int count = 0, *id = arg;
+
+	usleep(THREADS - *id);
+
+	cl_git_pass(git_reference_iterator_new(&i, g_repo));
+
+	for (count = 0; !git_reference_next(&ref, i); ++count) {
+		cl_assert(ref != NULL);
+		git_reference_free(ref);
+	}
+
+	if (g_expected > 0)
+		cl_assert_equal_i(g_expected, count);
+
+	git_reference_iterator_free(i);
+
+	return arg;
+}
+
+void test_threads_refdb__iterator(void)
+{
+	int r, t;
+	git_thread th[THREADS];
+	int id[THREADS];
+	git_oid head;
+	git_reference *ref;
+	char name[128];
+	git_refdb *refdb;
+
+	g_repo = cl_git_sandbox_init("testrepo2");
+
+	cl_git_pass(git_reference_name_to_id(&head, g_repo, "HEAD"));
+
+	/* make a bunch of references */
+
+	for (r = 0; r < 200; ++r) {
+		snprintf(name, sizeof(name), "refs/heads/direct-%03d", r);
+		cl_git_pass(git_reference_create(&ref, g_repo, name, &head, 0));
+		git_reference_free(ref);
+	}
+
+	cl_git_pass(git_repository_refdb(&refdb, g_repo));
+	cl_git_pass(git_refdb_compress(refdb));
+	git_refdb_free(refdb);
+
+	g_expected = 206;
+
+	for (r = 0; r < REPEAT; ++r) {
+		g_repo = cl_git_sandbox_reopen(); /* reopen to flush caches */
+
+		for (t = 0; t < THREADS; ++t) {
+			id[t] = t;
+			cl_git_pass(git_thread_create(&th[t], NULL, iterate_refs, &id[t]));
+		}
+
+		for (t = 0; t < THREADS; ++t) {
+			cl_git_pass(git_thread_join(th[t], NULL));
+		}
+
+		memset(th, 0, sizeof(th));
+	}
+}
+
+static void *create_refs(void *arg)
+{
+	int *id = arg, i;
+	git_oid head;
+	char name[128];
+	git_reference *ref[10];
+
+	cl_git_pass(git_reference_name_to_id(&head, g_repo, "HEAD"));
+
+	for (i = 0; i < 10; ++i) {
+		snprintf(name, sizeof(name), "refs/heads/thread-%03d-%02d", *id, i);
+		cl_git_pass(git_reference_create(&ref[i], g_repo, name, &head, 0));
+
+		if (i == 5) {
+			git_refdb *refdb;
+			cl_git_pass(git_repository_refdb(&refdb, g_repo));
+			cl_git_pass(git_refdb_compress(refdb));
+			git_refdb_free(refdb);
+		}
+	}
+
+	for (i = 0; i < 10; ++i)
+		git_reference_free(ref[i]);
+
+	return arg;
+}
+
+static void *delete_refs(void *arg)
+{
+	int *id = arg, i;
+	git_reference *ref;
+	char name[128];
+
+	for (i = 0; i < 10; ++i) {
+		snprintf(
+			name, sizeof(name), "refs/heads/thread-%03d-%02d", (*id) & ~0x3, i);
+
+		if (!git_reference_lookup(&ref, g_repo, name)) {
+			fprintf(stderr, "deleting %s\n", name);
+			cl_git_pass(git_reference_delete(ref));
+			git_reference_delete(ref);
+		}
+
+		if (i == 5) {
+			git_refdb *refdb;
+			cl_git_pass(git_repository_refdb(&refdb, g_repo));
+			cl_git_pass(git_refdb_compress(refdb));
+			git_refdb_free(refdb);
+		}
+	}
+
+	return arg;
+}
+
+void test_threads_refdb__edit_while_iterate(void)
+{
+	int r, t;
+	git_thread th[THREADS];
+	int id[THREADS];
+	git_oid head;
+	git_reference *ref;
+	char name[128];
+	git_refdb *refdb;
+
+	g_repo = cl_git_sandbox_init("testrepo2");
+
+	cl_git_pass(git_reference_name_to_id(&head, g_repo, "HEAD"));
+
+	/* make a bunch of references */
+
+	for (r = 0; r < 50; ++r) {
+		snprintf(name, sizeof(name), "refs/heads/starter-%03d", r);
+		cl_git_pass(git_reference_create(&ref, g_repo, name, &head, 0));
+		git_reference_free(ref);
+	}
+
+	cl_git_pass(git_repository_refdb(&refdb, g_repo));
+	cl_git_pass(git_refdb_compress(refdb));
+	git_refdb_free(refdb);
+
+	g_expected = -1;
+
+	g_repo = cl_git_sandbox_reopen(); /* reopen to flush caches */
+
+	for (t = 0; t < THREADS; ++t) {
+		void *(*fn)(void *arg);
+
+		switch (t & 0x3) {
+		case 0:  fn = create_refs;  break;
+		case 1:  fn = delete_refs;  break;
+		default: fn = iterate_refs; break;
+		}
+
+		id[t] = t;
+		cl_git_pass(git_thread_create(&th[t], NULL, fn, &id[t]));
+	}
+
+	for (t = 0; t < THREADS; ++t) {
+		cl_git_pass(git_thread_join(th[t], NULL));
+	}
+
+	memset(th, 0, sizeof(th));
+
+	for (t = 0; t < THREADS; ++t) {
+		id[t] = t;
+		cl_git_pass(git_thread_create(&th[t], NULL, iterate_refs, &id[t]));
+	}
+
+	for (t = 0; t < THREADS; ++t) {
+		cl_git_pass(git_thread_join(th[t], NULL));
+	}
+}