diff --git a/src/blame.c b/src/blame.c
index a52f9402b..08a90dcfd 100644
--- a/src/blame.c
+++ b/src/blame.c
@@ -331,7 +331,7 @@ static int blame_internal(git_blame *blame)
 
 	blame->ent = ent;
 
-	git_blame__like_git(blame, blame->options.flags);
+	error = git_blame__like_git(blame, blame->options.flags);
 
 cleanup:
 	for (ent = blame->ent; ent; ) {
diff --git a/src/blame_git.c b/src/blame_git.c
index f481426aa..67bae2384 100644
--- a/src/blame_git.c
+++ b/src/blame_git.c
@@ -9,6 +9,7 @@
 #include "commit.h"
 #include "blob.h"
 #include "xdiff/xinclude.h"
+#include "diff_xdiff.h"
 
 /*
  * Origin is refcounted and usually we keep the blob contents to be
@@ -351,6 +352,13 @@ static int diff_hunks(mmfile_t file_a, mmfile_t file_b, void *cb_data)
 	ecb.priv = cb_data;
 
 	trim_common_tail(&file_a, &file_b, 0);
+
+	if (file_a.size > GIT_XDIFF_MAX_SIZE ||
+		file_b.size > GIT_XDIFF_MAX_SIZE) {
+		giterr_set(GITERR_INVALID, "file too large to blame");
+		return -1;
+	}
+
 	return xdl_diff(&file_a, &file_b, &xpp, &xecfg, &ecb);
 }
 
@@ -379,7 +387,9 @@ static int pass_blame_to_parent(
 	fill_origin_blob(parent, &file_p);
 	fill_origin_blob(target, &file_o);
 
-	diff_hunks(file_p, file_o, &d);
+	if (diff_hunks(file_p, file_o, &d) < 0)
+		return -1;
+
 	/* The reset (i.e. anything after tlno) are the same as the parent */
 	blame_chunk(blame, d.tlno, d.plno, last_in_target, target, parent);
 
@@ -477,12 +487,13 @@ static void pass_whole_blame(git_blame *blame,
 	}
 }
 
-static void pass_blame(git_blame *blame, git_blame__origin *origin, uint32_t opt)
+static int pass_blame(git_blame *blame, git_blame__origin *origin, uint32_t opt)
 {
 	git_commit *commit = origin->commit;
 	int i, num_parents;
 	git_blame__origin *sg_buf[16];
 	git_blame__origin *porigin, **sg_origin = sg_buf;
+	int ret, error = 0;
 
 	num_parents = git_commit_parentcount(commit);
 	if (!git_oid_cmp(git_commit_id(commit), &blame->options.oldest_commit))
@@ -540,8 +551,13 @@ static void pass_blame(git_blame *blame, git_blame__origin *origin, uint32_t opt
 			origin_incref(porigin);
 			origin->previous = porigin;
 		}
-		if (pass_blame_to_parent(blame, origin, porigin))
+
+		if ((ret = pass_blame_to_parent(blame, origin, porigin)) != 0) {
+			if (ret < 0)
+				error = -1;
+
 			goto finish;
+		}
 	}
 
 	/* TODO: optionally find moves in parents' files */
@@ -554,7 +570,7 @@ finish:
 			origin_decref(sg_origin[i]);
 	if (sg_origin != sg_buf)
 		git__free(sg_origin);
-	return;
+	return error;
 }
 
 /*
@@ -583,7 +599,7 @@ static void coalesce(git_blame *blame)
 	}
 }
 
-void git_blame__like_git(git_blame *blame, uint32_t opt)
+int git_blame__like_git(git_blame *blame, uint32_t opt)
 {
 	while (true) {
 		git_blame__entry *ent;
@@ -594,11 +610,13 @@ void git_blame__like_git(git_blame *blame, uint32_t opt)
 			if (!ent->guilty)
 				suspect = ent->suspect;
 		if (!suspect)
-			return; /* all done */
+			return 0; /* all done */
 
 		/* We'll use this suspect later in the loop, so hold on to it for now. */
 		origin_incref(suspect);
-		pass_blame(blame, suspect, opt);
+
+		if (pass_blame(blame, suspect, opt) < 0)
+			return -1;
 
 		/* Take responsibility for the remaining entries */
 		for (ent = blame->ent; ent; ent = ent->next) {
@@ -613,6 +631,8 @@ void git_blame__like_git(git_blame *blame, uint32_t opt)
 	}
 
 	coalesce(blame);
+
+	return 0;
 }
 
 void git_blame__free_entry(git_blame__entry *ent)
diff --git a/src/blame_git.h b/src/blame_git.h
index 3ec2710b8..1891b0e1f 100644
--- a/src/blame_git.h
+++ b/src/blame_git.h
@@ -15,6 +15,6 @@ int git_blame__get_origin(
 		git_commit *commit,
 		const char *path);
 void git_blame__free_entry(git_blame__entry *ent);
-void git_blame__like_git(git_blame *sb, uint32_t flags);
+int git_blame__like_git(git_blame *sb, uint32_t flags);
 
 #endif
diff --git a/src/checkout.c b/src/checkout.c
index 2a8bfd558..632556622 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -18,6 +18,7 @@
 #include "git2/submodule.h"
 #include "git2/sys/index.h"
 #include "git2/sys/filter.h"
+#include "git2/merge.h"
 
 #include "refs.h"
 #include "repository.h"
@@ -27,7 +28,7 @@
 #include "diff.h"
 #include "pathspec.h"
 #include "buf_text.h"
-#include "merge_file.h"
+#include "diff_xdiff.h"
 #include "path.h"
 #include "attr.h"
 #include "pool.h"
diff --git a/src/common.h b/src/common.h
index 6dca36fbd..7170df91a 100644
--- a/src/common.h
+++ b/src/common.h
@@ -208,6 +208,15 @@ GIT_INLINE(void) git__init_structure(void *structure, size_t len, unsigned int v
 #define GITERR_CHECK_ALLOC_ADD(out, one, two) \
 	if (GIT_ADD_SIZET_OVERFLOW(out, one, two)) { return -1; }
 
+#define GITERR_CHECK_ALLOC_ADD3(out, one, two, three) \
+	if (GIT_ADD_SIZET_OVERFLOW(out, one, two) || \
+		GIT_ADD_SIZET_OVERFLOW(out, *(out), three)) { return -1; }
+
+#define GITERR_CHECK_ALLOC_ADD4(out, one, two, three, four) \
+	if (GIT_ADD_SIZET_OVERFLOW(out, one, two) || \
+		GIT_ADD_SIZET_OVERFLOW(out, *(out), three) || \
+		GIT_ADD_SIZET_OVERFLOW(out, *(out), four)) { return -1; }
+
 /** Check for multiplicative overflow, failing if it would occur. */
 #define GITERR_CHECK_ALLOC_MULTIPLY(out, nelem, elsize) \
 	if (GIT_MULTIPLY_SIZET_OVERFLOW(out, nelem, elsize)) { return -1; }
diff --git a/src/diff_patch.c b/src/diff_patch.c
index 0628da6f2..50faa3b3f 100644
--- a/src/diff_patch.c
+++ b/src/diff_patch.c
@@ -30,6 +30,10 @@ static void diff_patch_update_binary(git_patch *patch)
 		(patch->nfile.file->flags & GIT_DIFF_FLAG_BINARY) != 0)
 		patch->delta->flags |= GIT_DIFF_FLAG_BINARY;
 
+	else if (patch->ofile.file->size > GIT_XDIFF_MAX_SIZE ||
+			 patch->nfile.file->size > GIT_XDIFF_MAX_SIZE)
+		patch->delta->flags |= GIT_DIFF_FLAG_BINARY;
+
 	else if ((patch->ofile.file->flags & DIFF_FLAGS_NOT_BINARY) != 0 &&
 			 (patch->nfile.file->flags & DIFF_FLAGS_NOT_BINARY) != 0)
 		patch->delta->flags |= GIT_DIFF_FLAG_NOT_BINARY;
diff --git a/src/diff_xdiff.c b/src/diff_xdiff.c
index e5984f1c9..1057df3aa 100644
--- a/src/diff_xdiff.c
+++ b/src/diff_xdiff.c
@@ -4,6 +4,7 @@
  * This file is part of libgit2, distributed under the GNU GPL v2 with
  * a Linking Exception. For full terms see the included COPYING file.
  */
+#include "git2/errors.h"
 #include "common.h"
 #include "diff.h"
 #include "diff_driver.h"
@@ -208,6 +209,12 @@ static int git_xdiff(git_diff_output *output, git_patch *patch)
 	git_patch__old_data(&info.xd_old_data.ptr, &info.xd_old_data.size, patch);
 	git_patch__new_data(&info.xd_new_data.ptr, &info.xd_new_data.size, patch);
 
+	if (info.xd_old_data.size > GIT_XDIFF_MAX_SIZE ||
+		info.xd_new_data.size > GIT_XDIFF_MAX_SIZE) {
+		giterr_set(GITERR_INVALID, "files too large for diff");
+		return -1;
+	}
+
 	xdl_diff(&info.xd_old_data, &info.xd_new_data,
 		&xo->params, &xo->config, &xo->callback);
 
diff --git a/src/diff_xdiff.h b/src/diff_xdiff.h
index c547b00cf..98e11b2cb 100644
--- a/src/diff_xdiff.h
+++ b/src/diff_xdiff.h
@@ -11,6 +11,11 @@
 #include "diff_patch.h"
 #include "xdiff/xdiff.h"
 
+/* xdiff cannot cope with large files.  these files should not be passed to
+ * xdiff.  callers should treat these large files as binary.
+ */
+#define GIT_XDIFF_MAX_SIZE (1024LL * 1024 * 1023)
+
 /* A git_xdiff_output is a git_diff_output with extra fields necessary
  * to use libxdiff.  Calling git_xdiff_init() will set the diff_cb field
  * of the output to use xdiff to generate the diffs.
diff --git a/src/merge.c b/src/merge.c
index fc5088c82..930457bdb 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -20,7 +20,6 @@
 #include "diff.h"
 #include "checkout.h"
 #include "tree.h"
-#include "merge_file.h"
 #include "blob.h"
 #include "oid.h"
 #include "index.h"
@@ -61,12 +60,6 @@ struct merge_diff_df_data {
 	git_merge_diff *prev_conflict;
 };
 
-GIT_INLINE(int) merge_diff_detect_binary(
-	bool *binary_out,
-	git_repository *repo,
-	const git_merge_diff *conflict);
-
-
 /* Merge base computation */
 
 int merge_bases_many(git_commit_list **out, git_revwalk **walk_out, git_repository *repo, size_t length, const git_oid input_array[])
@@ -668,7 +661,6 @@ static int merge_conflict_resolve_automerge(
 	git_odb *odb = NULL;
 	git_oid automerge_oid;
 	int error = 0;
-	bool binary = false;
 
 	assert(resolved && diff_list && conflict);
 
@@ -703,12 +695,6 @@ static int merge_conflict_resolve_automerge(
 		strcmp(conflict->ancestor_entry.path, conflict->their_entry.path) != 0)
 		return 0;
 
-	/* Reject binary conflicts */
-	if ((error = merge_diff_detect_binary(&binary, diff_list->repo, conflict)) < 0)
-		return error;
-	if (binary)
-		return 0;
-
 	ancestor = GIT_MERGE_INDEX_ENTRY_EXISTS(conflict->ancestor_entry) ?
 		&conflict->ancestor_entry : NULL;
 	ours = GIT_MERGE_INDEX_ENTRY_EXISTS(conflict->our_entry) ?
@@ -1314,48 +1300,6 @@ GIT_INLINE(int) merge_diff_detect_type(
 	return 0;
 }
 
-GIT_INLINE(int) merge_diff_detect_binary(
-	bool *binary_out,
-	git_repository *repo,
-	const git_merge_diff *conflict)
-{
-	git_blob *ancestor_blob = NULL, *our_blob = NULL, *their_blob = NULL;
-	int error = 0;
-	bool binary = false;
-
-	if (GIT_MERGE_INDEX_ENTRY_ISFILE(conflict->ancestor_entry)) {
-		if ((error = git_blob_lookup(&ancestor_blob, repo, &conflict->ancestor_entry.id)) < 0)
-			goto done;
-
-		binary = git_blob_is_binary(ancestor_blob);
-	}
-
-	if (!binary &&
-		GIT_MERGE_INDEX_ENTRY_ISFILE(conflict->our_entry)) {
-		if ((error = git_blob_lookup(&our_blob, repo, &conflict->our_entry.id)) < 0)
-			goto done;
-
-		binary = git_blob_is_binary(our_blob);
-	}
-
-	if (!binary &&
-		GIT_MERGE_INDEX_ENTRY_ISFILE(conflict->their_entry)) {
-		if ((error = git_blob_lookup(&their_blob, repo, &conflict->their_entry.id)) < 0)
-			goto done;
-
-		binary = git_blob_is_binary(their_blob);
-	}
-
-	*binary_out = binary;
-
-done:
-	git_blob_free(ancestor_blob);
-	git_blob_free(our_blob);
-	git_blob_free(their_blob);
-
-	return error;
-}
-
 GIT_INLINE(int) index_entry_dup_pool(
 	git_index_entry *out,
 	git_pool *pool,
diff --git a/src/merge_file.c b/src/merge_file.c
index 6d89b089d..6d4738065 100644
--- a/src/merge_file.c
+++ b/src/merge_file.c
@@ -7,17 +7,23 @@
 
 #include "common.h"
 #include "repository.h"
-#include "merge_file.h"
 #include "posix.h"
 #include "fileops.h"
 #include "index.h"
+#include "diff_xdiff.h"
 
 #include "git2/repository.h"
 #include "git2/object.h"
 #include "git2/index.h"
+#include "git2/merge.h"
 
 #include "xdiff/xdiff.h"
 
+/* only examine the first 8000 bytes for binaryness.
+ * https://github.com/git/git/blob/77bd3ea9f54f1584147b594abc04c26ca516d987/xdiff-interface.c#L197
+ */
+#define GIT_MERGE_FILE_BINARY_SIZE 8000
+
 #define GIT_MERGE_FILE_SIDE_EXISTS(X)	((X)->mode != 0)
 
 GIT_INLINE(const char *) merge_file_best_path(
@@ -100,7 +106,7 @@ static void merge_file_normalize_opts(
 	}
 }
 
-static int git_merge_file__from_inputs(
+static int merge_file__xdiff(
 	git_merge_file_result *out,
 	const git_merge_file_input *ancestor,
 	const git_merge_file_input *ours,
@@ -189,6 +195,63 @@ done:
 	return error;
 }
 
+static bool merge_file__is_binary(const git_merge_file_input *file)
+{
+	size_t len = file ? file->size : 0;
+
+	if (len > GIT_XDIFF_MAX_SIZE)
+		return true;
+	if (len > GIT_MERGE_FILE_BINARY_SIZE)
+		len = GIT_MERGE_FILE_BINARY_SIZE;
+
+	return len ? (memchr(file->ptr, 0, len) != NULL) : false;
+}
+
+static int merge_file__binary(
+	git_merge_file_result *out,
+	const git_merge_file_input *ours,
+	const git_merge_file_input *theirs,
+	const git_merge_file_options *given_opts)
+{
+	const git_merge_file_input *favored = NULL;
+
+	memset(out, 0x0, sizeof(git_merge_file_result));
+
+	if (given_opts && given_opts->favor == GIT_MERGE_FILE_FAVOR_OURS)
+		favored = ours;
+	else if (given_opts && given_opts->favor == GIT_MERGE_FILE_FAVOR_THEIRS)
+		favored = theirs;
+	else
+		goto done;
+
+	if ((out->path = git__strdup(favored->path)) == NULL ||
+		(out->ptr = git__malloc(favored->size)) == NULL)
+		goto done;
+
+	memcpy((char *)out->ptr, favored->ptr, favored->size);
+	out->len = favored->size;
+	out->mode = favored->mode;
+	out->automergeable = 1;
+
+done:
+	return 0;
+}
+
+static int merge_file__from_inputs(
+	git_merge_file_result *out,
+	const git_merge_file_input *ancestor,
+	const git_merge_file_input *ours,
+	const git_merge_file_input *theirs,
+	const git_merge_file_options *given_opts)
+{
+	if (merge_file__is_binary(ancestor) ||
+		merge_file__is_binary(ours) ||
+		merge_file__is_binary(theirs))
+		return merge_file__binary(out, ours, theirs, given_opts);
+
+	return merge_file__xdiff(out, ancestor, ours, theirs, given_opts);
+}
+
 static git_merge_file_input *git_merge_file__normalize_inputs(
 	git_merge_file_input *out,
 	const git_merge_file_input *given)
@@ -223,7 +286,7 @@ int git_merge_file(
 	ours = git_merge_file__normalize_inputs(&inputs[1], ours);
 	theirs = git_merge_file__normalize_inputs(&inputs[2], theirs);
 
-	return git_merge_file__from_inputs(out, ancestor, ours, theirs, options);
+	return merge_file__from_inputs(out, ancestor, ours, theirs, options);
 }
 
 int git_merge_file_from_index(
@@ -234,8 +297,8 @@ int git_merge_file_from_index(
 	const git_index_entry *theirs,
 	const git_merge_file_options *options)
 {
-	git_merge_file_input inputs[3] = { {0} },
-		*ancestor_input = NULL, *our_input = NULL, *their_input = NULL;
+	git_merge_file_input *ancestor_ptr = NULL,
+		ancestor_input = {0}, our_input = {0}, their_input = {0};
 	git_odb *odb = NULL;
 	git_odb_object *odb_object[3] = { 0 };
 	int error = 0;
@@ -249,27 +312,20 @@ int git_merge_file_from_index(
 
 	if (ancestor) {
 		if ((error = git_merge_file__input_from_index(
-			&inputs[0], &odb_object[0], odb, ancestor)) < 0)
+			&ancestor_input, &odb_object[0], odb, ancestor)) < 0)
 			goto done;
 
-		ancestor_input = &inputs[0];
+		ancestor_ptr = &ancestor_input;
 	}
 
 	if ((error = git_merge_file__input_from_index(
-		&inputs[1], &odb_object[1], odb, ours)) < 0)
+			&our_input, &odb_object[1], odb, ours)) < 0 ||
+		(error = git_merge_file__input_from_index(
+			&their_input, &odb_object[2], odb, theirs)) < 0)
 		goto done;
 
-	our_input = &inputs[1];
-
-	if ((error = git_merge_file__input_from_index(
-		&inputs[2], &odb_object[2], odb, theirs)) < 0)
-		goto done;
-
-	their_input = &inputs[2];
-
-	if ((error = git_merge_file__from_inputs(out,
-		ancestor_input, our_input, their_input, options)) < 0)
-		goto done;
+	error = merge_file__from_inputs(out,
+		ancestor_ptr, &our_input, &their_input, options);
 
 done:
 	git_odb_object_free(odb_object[0]);
@@ -286,7 +342,5 @@ void git_merge_file_result_free(git_merge_file_result *result)
 		return;
 
 	git__free((char *)result->path);
-
-	/* xdiff uses malloc() not git_malloc, so we use free(), not git_free() */
-	free((char *)result->ptr);
+	git__free((char *)result->ptr);
 }
diff --git a/src/merge_file.h b/src/merge_file.h
deleted file mode 100644
index 263391ee3..000000000
--- a/src/merge_file.h
+++ /dev/null
@@ -1,14 +0,0 @@
-/*
- * Copyright (C) the libgit2 contributors. All rights reserved.
- *
- * This file is part of libgit2, distributed under the GNU GPL v2 with
- * a Linking Exception. For full terms see the included COPYING file.
- */
-#ifndef INCLUDE_filediff_h__
-#define INCLUDE_filediff_h__
-
-#include "xdiff/xdiff.h"
-
-#include "git2/merge.h"
-
-#endif
diff --git a/src/xdiff/xdiff.h b/src/xdiff/xdiff.h
index e2f1e892b..db5d59884 100644
--- a/src/xdiff/xdiff.h
+++ b/src/xdiff/xdiff.h
@@ -20,6 +20,8 @@
  *
  */
 
+#include "util.h"
+
 #if !defined(XDIFF_H)
 #define XDIFF_H
 
@@ -106,9 +108,9 @@ typedef struct s_bdiffparam {
 } bdiffparam_t;
 
 
-#define xdl_malloc(x) malloc(x)
-#define xdl_free(ptr) free(ptr)
-#define xdl_realloc(ptr,x) realloc(ptr,x)
+#define xdl_malloc(x) git__malloc(x)
+#define xdl_free(ptr) git__free(ptr)
+#define xdl_realloc(ptr,x) git__realloc(ptr,x)
 
 void *xdl_mmfile_first(mmfile_t *mmf, long *size);
 long xdl_mmfile_size(mmfile_t *mmf);
diff --git a/src/xdiff/xdiffi.c b/src/xdiff/xdiffi.c
index 0620e5fff..f4d01b48c 100644
--- a/src/xdiff/xdiffi.c
+++ b/src/xdiff/xdiffi.c
@@ -21,7 +21,8 @@
  */
 
 #include "xinclude.h"
-
+#include "common.h"
+#include "integer.h"
 
 
 #define XDL_MAX_COST_MIN 256
@@ -323,7 +324,7 @@ int xdl_recs_cmp(diffdata_t *dd1, long off1, long lim1,
 
 int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 		xdfenv_t *xe) {
-	long ndiags;
+	size_t ndiags, allocsize;
 	long *kvd, *kvdf, *kvdb;
 	xdalgoenv_t xenv;
 	diffdata_t dd1, dd2;
@@ -343,9 +344,12 @@ int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	 * Allocate and setup K vectors to be used by the differential algorithm.
 	 * One is to store the forward path and one to store the backward path.
 	 */
-	ndiags = xe->xdf1.nreff + xe->xdf2.nreff + 3;
-	if (!(kvd = (long *) xdl_malloc((2 * ndiags + 2) * sizeof(long)))) {
+	GITERR_CHECK_ALLOC_ADD3(&ndiags, xe->xdf1.nreff, xe->xdf2.nreff, 3);
+	GITERR_CHECK_ALLOC_MULTIPLY(&allocsize, ndiags, 2);
+	GITERR_CHECK_ALLOC_ADD(&allocsize, allocsize, 2);
+	GITERR_CHECK_ALLOC_MULTIPLY(&allocsize, allocsize, sizeof(long));
 
+	if (!(kvd = (long *) xdl_malloc(allocsize))) {
 		xdl_free_env(xe);
 		return -1;
 	}
diff --git a/src/xdiff/xhistogram.c b/src/xdiff/xhistogram.c
index 500d8112a..0c2edb89c 100644
--- a/src/xdiff/xhistogram.c
+++ b/src/xdiff/xhistogram.c
@@ -44,6 +44,7 @@
 #include "xinclude.h"
 #include "xtypes.h"
 #include "xdiff.h"
+#include "common.h"
 
 #define MAX_PTR	UINT_MAX
 #define MAX_CNT	UINT_MAX
@@ -271,7 +272,7 @@ static int histogram_diff(
 {
 	struct histindex index;
 	struct region lcs;
-	unsigned int sz;
+	size_t sz;
 	int result = -1;
 
 	if (count1 <= 0 && count2 <= 0)
@@ -302,7 +303,8 @@ static int histogram_diff(
 
 	index.table_bits = xdl_hashbits(count1);
 	sz = index.records_size = 1 << index.table_bits;
-	sz *= sizeof(struct record *);
+	GITERR_CHECK_ALLOC_MULTIPLY(&sz, sz, sizeof(struct record *));
+
 	if (!(index.records = (struct record **) xdl_malloc(sz)))
 		goto cleanup;
 	memset(index.records, 0, sz);
diff --git a/src/xdiff/xmerge.c b/src/xdiff/xmerge.c
index b11e59817..7b7e0e2d3 100644
--- a/src/xdiff/xmerge.c
+++ b/src/xdiff/xmerge.c
@@ -21,6 +21,7 @@
  */
 
 #include "xinclude.h"
+#include "common.h"
 
 typedef struct s_xdmerge {
 	struct s_xdmerge *next;
@@ -109,59 +110,74 @@ static int xdl_merge_cmp_lines(xdfenv_t *xe1, int i1, xdfenv_t *xe2, int i2,
 	return 0;
 }
 
-static int xdl_recs_copy_0(int use_orig, xdfenv_t *xe, int i, int count, int add_nl, char *dest)
+static int xdl_recs_copy_0(size_t *out, int use_orig, xdfenv_t *xe, int i, int count, int add_nl, char *dest)
 {
 	xrecord_t **recs;
-	int size = 0;
+	size_t size = 0;
+
+	*out = 0;
 
 	recs = (use_orig ? xe->xdf1.recs : xe->xdf2.recs) + i;
 
 	if (count < 1)
 		return 0;
 
-	for (i = 0; i < count; size += recs[i++]->size)
+	for (i = 0; i < count; ) {
 		if (dest)
 			memcpy(dest + size, recs[i]->ptr, recs[i]->size);
+
+		GITERR_CHECK_ALLOC_ADD(&size, size, recs[i++]->size);
+	}
+
 	if (add_nl) {
 		i = recs[count - 1]->size;
 		if (i == 0 || recs[count - 1]->ptr[i - 1] != '\n') {
 			if (dest)
 				dest[size] = '\n';
-			size++;
+
+			GITERR_CHECK_ALLOC_ADD(&size, size, 1);
 		}
 	}
-	return size;
+
+	*out = size;
+	return 0;
 }
 
-static int xdl_recs_copy(xdfenv_t *xe, int i, int count, int add_nl, char *dest)
+static int xdl_recs_copy(size_t *out, xdfenv_t *xe, int i, int count, int add_nl, char *dest)
 {
-	return xdl_recs_copy_0(0, xe, i, count, add_nl, dest);
+	return xdl_recs_copy_0(out, 0, xe, i, count, add_nl, dest);
 }
 
-static int xdl_orig_copy(xdfenv_t *xe, int i, int count, int add_nl, char *dest)
+static int xdl_orig_copy(size_t *out, xdfenv_t *xe, int i, int count, int add_nl, char *dest)
 {
-	return xdl_recs_copy_0(1, xe, i, count, add_nl, dest);
+	return xdl_recs_copy_0(out, 1, xe, i, count, add_nl, dest);
 }
 
-static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
+static int fill_conflict_hunk(size_t *out, xdfenv_t *xe1, const char *name1,
 			      xdfenv_t *xe2, const char *name2,
 			      const char *name3,
-			      int size, int i, int style,
+			      size_t size, int i, int style,
 			      xdmerge_t *m, char *dest, int marker_size)
 {
 	int marker1_size = (name1 ? (int)strlen(name1) + 1 : 0);
 	int marker2_size = (name2 ? (int)strlen(name2) + 1 : 0);
 	int marker3_size = (name3 ? (int)strlen(name3) + 1 : 0);
+	size_t copied;
+
+	*out = 0;
 
 	if (marker_size <= 0)
 		marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
 
 	/* Before conflicting part */
-	size += xdl_recs_copy(xe1, i, m->i1 - i, 0,
-			      dest ? dest + size : NULL);
+	if (xdl_recs_copy(&copied, xe1, i, m->i1 - i, 0,
+			      dest ? dest + size : NULL) < 0)
+		return -1;
+
+	GITERR_CHECK_ALLOC_ADD(&size, size, copied);
 
 	if (!dest) {
-		size += marker_size + 1 + marker1_size;
+		GITERR_CHECK_ALLOC_ADD4(&size, size, marker_size, 1, marker1_size);
 	} else {
 		memset(dest + size, '<', marker_size);
 		size += marker_size;
@@ -174,13 +190,16 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 	}
 
 	/* Postimage from side #1 */
-	size += xdl_recs_copy(xe1, m->i1, m->chg1, 1,
-			      dest ? dest + size : NULL);
+	if (xdl_recs_copy(&copied, xe1, m->i1, m->chg1, 1,
+			      dest ? dest + size : NULL) < 0)
+		return -1;
+
+	GITERR_CHECK_ALLOC_ADD(&size, size, copied);
 
 	if (style == XDL_MERGE_DIFF3) {
 		/* Shared preimage */
 		if (!dest) {
-			size += marker_size + 1 + marker3_size;
+			GITERR_CHECK_ALLOC_ADD4(&size, size, marker_size, 1, marker3_size);
 		} else {
 			memset(dest + size, '|', marker_size);
 			size += marker_size;
@@ -191,12 +210,15 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 			}
 			dest[size++] = '\n';
 		}
-		size += xdl_orig_copy(xe1, m->i0, m->chg0, 1,
-				      dest ? dest + size : NULL);
+
+		if (xdl_orig_copy(&copied, xe1, m->i0, m->chg0, 1,
+				      dest ? dest + size : NULL) < 0)
+			return -1;
+		GITERR_CHECK_ALLOC_ADD(&size, size, copied);
 	}
 
 	if (!dest) {
-		size += marker_size + 1;
+		GITERR_CHECK_ALLOC_ADD3(&size, size, marker_size, 1);
 	} else {
 		memset(dest + size, '=', marker_size);
 		size += marker_size;
@@ -204,10 +226,14 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 	}
 
 	/* Postimage from side #2 */
-	size += xdl_recs_copy(xe2, m->i2, m->chg2, 1,
-			      dest ? dest + size : NULL);
+
+	if (xdl_recs_copy(&copied, xe2, m->i2, m->chg2, 1,
+			      dest ? dest + size : NULL) < 0)
+		return -1;
+	GITERR_CHECK_ALLOC_ADD(&size, size, copied);
+
 	if (!dest) {
-		size += marker_size + 1 + marker2_size;
+		GITERR_CHECK_ALLOC_ADD4(&size, size, marker_size, 1, marker2_size);
 	} else {
 		memset(dest + size, '>', marker_size);
 		size += marker_size;
@@ -218,46 +244,69 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
 		}
 		dest[size++] = '\n';
 	}
-	return size;
+
+	*out = size;
+	return 0;
 }
 
-static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
+static int xdl_fill_merge_buffer(size_t *out,
+				 xdfenv_t *xe1, const char *name1,
 				 xdfenv_t *xe2, const char *name2,
 				 const char *ancestor_name,
 				 int favor,
 				 xdmerge_t *m, char *dest, int style,
 				 int marker_size)
 {
-	int size, i;
+	size_t size, copied;
+	int i;
+
+	*out = 0;
 
 	for (size = i = 0; m; m = m->next) {
 		if (favor && !m->mode)
 			m->mode = favor;
 
-		if (m->mode == 0)
-			size = fill_conflict_hunk(xe1, name1, xe2, name2,
+		if (m->mode == 0) {
+			if (fill_conflict_hunk(&size, xe1, name1, xe2, name2,
 						  ancestor_name,
 						  size, i, style, m, dest,
-						  marker_size);
+						  marker_size) < 0)
+				return -1;
+		}
 		else if (m->mode & 3) {
 			/* Before conflicting part */
-			size += xdl_recs_copy(xe1, i, m->i1 - i, 0,
-					      dest ? dest + size : NULL);
+			if (xdl_recs_copy(&copied, xe1, i, m->i1 - i, 0,
+					      dest ? dest + size : NULL) < 0)
+				return -1;
+			GITERR_CHECK_ALLOC_ADD(&size, size, copied);
+
 			/* Postimage from side #1 */
-			if (m->mode & 1)
-				size += xdl_recs_copy(xe1, m->i1, m->chg1, (m->mode & 2),
-						      dest ? dest + size : NULL);
+			if (m->mode & 1) {
+				if (xdl_recs_copy(&copied, xe1, m->i1, m->chg1, (m->mode & 2),
+						      dest ? dest + size : NULL) < 0)
+					return -1;
+				GITERR_CHECK_ALLOC_ADD(&size, size, copied);
+			}
+
 			/* Postimage from side #2 */
-			if (m->mode & 2)
-				size += xdl_recs_copy(xe2, m->i2, m->chg2, 0,
-						      dest ? dest + size : NULL);
+			if (m->mode & 2) {
+				if (xdl_recs_copy(&copied, xe2, m->i2, m->chg2, 0,
+						      dest ? dest + size : NULL) < 0)
+					return -1;
+				GITERR_CHECK_ALLOC_ADD(&size, size, copied);
+			}
 		} else
 			continue;
 		i = m->i1 + m->chg1;
 	}
-	size += xdl_recs_copy(xe1, i, xe1->xdf2.nrec - i, 0,
-			      dest ? dest + size : NULL);
-	return size;
+
+	if (xdl_recs_copy(&copied, xe1, i, xe1->xdf2.nrec - i, 0,
+			      dest ? dest + size : NULL) < 0)
+		return -1;
+	GITERR_CHECK_ALLOC_ADD(&size, size, copied);
+
+	*out = size;
+	return 0;
 }
 
 /*
@@ -551,19 +600,24 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
 	/* output */
 	if (result) {
 		int marker_size = xmp->marker_size;
-		int size = xdl_fill_merge_buffer(xe1, name1, xe2, name2,
+		size_t size;
+
+		if (xdl_fill_merge_buffer(&size, xe1, name1, xe2, name2,
 						 ancestor_name,
 						 favor, changes, NULL, style,
-						 marker_size);
+						 marker_size) < 0)
+			return -1;
+
 		result->ptr = xdl_malloc(size);
 		if (!result->ptr) {
 			xdl_cleanup_merge(changes);
 			return -1;
 		}
 		result->size = size;
-		xdl_fill_merge_buffer(xe1, name1, xe2, name2,
+		if (xdl_fill_merge_buffer(&size, xe1, name1, xe2, name2,
 				      ancestor_name, favor, changes,
-				      result->ptr, style, marker_size);
+				      result->ptr, style, marker_size) < 0)
+			return -1;
 	}
 	return xdl_cleanup_merge(changes);
 }
diff --git a/tests/merge/files.c b/tests/merge/files.c
index 2fd90d066..2d55df2b2 100644
--- a/tests/merge/files.c
+++ b/tests/merge/files.c
@@ -6,6 +6,7 @@
 #include "merge_helpers.h"
 #include "refs.h"
 #include "fileops.h"
+#include "diff_xdiff.h"
 
 #define TEST_REPO_PATH "merge-resolve"
 #define TEST_INDEX_PATH TEST_REPO_PATH "/.git/index"
@@ -288,3 +289,90 @@ void test_merge_files__doesnt_add_newline(void)
 	git_merge_file_result_free(&result);
 }
 
+void test_merge_files__skips_large_files(void)
+{
+	git_merge_file_input ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_options opts = GIT_MERGE_FILE_OPTIONS_INIT;
+	git_merge_file_result result = {0};
+
+	ours.size = GIT_XDIFF_MAX_SIZE + 1;
+	ours.path = "testfile.txt";
+	ours.mode = 0100755;
+
+	theirs.size = GIT_XDIFF_MAX_SIZE + 1;
+	theirs.path = "testfile.txt";
+	theirs.mode = 0100755;
+
+	cl_git_pass(git_merge_file(&result, NULL, &ours, &theirs, &opts));
+
+	cl_assert_equal_i(0, result.automergeable);
+
+	git_merge_file_result_free(&result);
+}
+
+void test_merge_files__skips_binaries(void)
+{
+	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
+		ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_result result = {0};
+
+	ancestor.ptr = "ance\0stor\0";
+	ancestor.size = 10;
+	ancestor.path = "ancestor.txt";
+	ancestor.mode = 0100755;
+
+	ours.ptr = "foo\0bar\0";
+	ours.size = 8;
+	ours.path = "ours.txt";
+	ours.mode = 0100755;
+
+	theirs.ptr = "bar\0foo\0";
+	theirs.size = 8;
+	theirs.path = "theirs.txt";
+	theirs.mode = 0100644;
+
+	cl_git_pass(git_merge_file(&result, &ancestor, &ours, &theirs, NULL));
+
+	cl_assert_equal_i(0, result.automergeable);
+
+	git_merge_file_result_free(&result);
+}
+
+void test_merge_files__handles_binaries_when_favored(void)
+{
+	git_merge_file_input ancestor = GIT_MERGE_FILE_INPUT_INIT,
+		ours = GIT_MERGE_FILE_INPUT_INIT,
+		theirs = GIT_MERGE_FILE_INPUT_INIT;
+	git_merge_file_options opts = GIT_MERGE_FILE_OPTIONS_INIT;
+	git_merge_file_result result = {0};
+
+	ancestor.ptr = "ance\0stor\0";
+	ancestor.size = 10;
+	ancestor.path = "ancestor.txt";
+	ancestor.mode = 0100755;
+
+	ours.ptr = "foo\0bar\0";
+	ours.size = 8;
+	ours.path = "ours.txt";
+	ours.mode = 0100755;
+
+	theirs.ptr = "bar\0foo\0";
+	theirs.size = 8;
+	theirs.path = "theirs.txt";
+	theirs.mode = 0100644;
+
+	opts.favor = GIT_MERGE_FILE_FAVOR_OURS;
+	cl_git_pass(git_merge_file(&result, &ancestor, &ours, &theirs, &opts));
+
+	cl_assert_equal_i(1, result.automergeable);
+
+	cl_assert_equal_s("ours.txt", result.path);
+	cl_assert_equal_i(0100755, result.mode);
+
+	cl_assert_equal_i(ours.size, result.len);
+	cl_assert(memcmp(result.ptr, ours.ptr, ours.size) == 0);
+
+	git_merge_file_result_free(&result);
+}