diff --git a/include/git2/attr.h b/include/git2/attr.h
index fad7183da..73a625a7e 100644
--- a/include/git2/attr.h
+++ b/include/git2/attr.h
@@ -172,18 +172,17 @@ GIT_EXTERN(int) git_attr_get_many(
  *
  * @param repo The repository containing the path.
  * @param flags A combination of GIT_ATTR_CHECK... flags.
- * @param path The path inside the repo to check attributes.  This
- *             does not have to exist, but if it does not, then
- *             it will be treated as a plain file (i.e. not a directory).
- * @param callback The function that will be invoked on each attribute
- *             and attribute value.  The name parameter will be the name
- *             of the attribute and the value will be the value it is
- *             set to, including possibly NULL if the attribute is
- *             explicitly set to UNSPECIFIED using the ! sign.  This
- *             will be invoked only once per attribute name, even if
- *             there are multiple rules for a given file.  The highest
- *             priority rule will be used.
+ * @param path Path inside the repo to check attributes.  This does not have
+ *             to exist, but if it does not, then it will be treated as a
+ *             plain file (i.e. not a directory).
+ * @param callback Function to invoke on each attribute name and value.  The
+ *             value may be NULL is the attribute is explicitly set to
+ *             UNSPECIFIED using the '!' sign.  Callback will be invoked
+ *             only once per attribute name, even if there are multiple
+ *             rules for a given file.  The highest priority rule will be
+ *             used.  Return a non-zero value from this to stop looping.
  * @param payload Passed on as extra parameter to callback function.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_attr_foreach(
 	git_repository *repo,
diff --git a/include/git2/branch.h b/include/git2/branch.h
index 8884df15a..c8f2d8f5f 100644
--- a/include/git2/branch.h
+++ b/include/git2/branch.h
@@ -74,6 +74,8 @@ GIT_EXTERN(int) git_branch_delete(
 /**
  * Loop over all the branches and issue a callback for each one.
  *
+ * If the callback returns a non-zero value, this will stop looping.
+ *
  * @param repo Repository where to find the branches.
  *
  * @param list_flags Filtering flags for the branch
@@ -84,7 +86,7 @@ GIT_EXTERN(int) git_branch_delete(
  *
  * @param payload Extra parameter to callback function.
  *
- * @return 0 or an error code.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_branch_foreach(
 		git_repository *repo,
diff --git a/include/git2/config.h b/include/git2/config.h
index c46e7fc9d..8a36885c7 100644
--- a/include/git2/config.h
+++ b/include/git2/config.h
@@ -302,12 +302,12 @@ GIT_EXTERN(int) git_config_delete(git_config *cfg, const char *name);
  * The callback receives the normalized name and value of each variable
  * in the config backend, and the data pointer passed to this function.
  * As soon as one of the callback functions returns something other than 0,
- * this function returns that value.
+ * this function stops iterating and returns `GIT_EUSER`.
  *
  * @param cfg where to get the variables from
  * @param callback the function to call on each variable
  * @param payload the data to pass to the callback
- * @return 0 or the return value of the callback which didn't return 0
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_config_foreach(
 	git_config *cfg,
diff --git a/include/git2/diff.h b/include/git2/diff.h
index 85727d969..79ef7a49b 100644
--- a/include/git2/diff.h
+++ b/include/git2/diff.h
@@ -332,6 +332,9 @@ GIT_EXTERN(int) git_diff_merge(
  * callbacks will not be invoked for binary files on the diff list or for
  * files whose only changed is a file mode change.
  *
+ * Returning a non-zero value from any of the callbacks will terminate
+ * the iteration and cause this return `GIT_EUSER`.
+ *
  * @param diff A git_diff_list generated by one of the above functions.
  * @param cb_data Reference pointer that will be passed to your callbacks.
  * @param file_cb Callback function to make per file in the diff.
@@ -341,6 +344,7 @@ GIT_EXTERN(int) git_diff_merge(
  * @param line_cb Optional callback to make per line of diff text.  This
  *                same callback will be made for context lines, added, and
  *                removed lines, and even for a deleted trailing newline.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_diff_foreach(
 	git_diff_list *diff,
@@ -351,6 +355,14 @@ GIT_EXTERN(int) git_diff_foreach(
 
 /**
  * Iterate over a diff generating text output like "git diff --name-status".
+ *
+ * Returning a non-zero value from the callbacks will terminate the
+ * iteration and cause this return `GIT_EUSER`.
+ *
+ * @param diff A git_diff_list generated by one of the above functions.
+ * @param cb_data Reference pointer that will be passed to your callback.
+ * @param print_cb Callback to make per line of diff text.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_diff_print_compact(
 	git_diff_list *diff,
@@ -362,6 +374,9 @@ GIT_EXTERN(int) git_diff_print_compact(
  *
  * This is a super easy way to generate a patch from a diff.
  *
+ * Returning a non-zero value from the callbacks will terminate the
+ * iteration and cause this return `GIT_EUSER`.
+ *
  * @param diff A git_diff_list generated by one of the above functions.
  * @param cb_data Reference pointer that will be passed to your callbacks.
  * @param print_cb Callback function to output lines of the diff.  This
@@ -369,6 +384,7 @@ GIT_EXTERN(int) git_diff_print_compact(
  *                 headers, and diff lines.  Fortunately, you can probably
  *                 use various GIT_DIFF_LINE constants to determine what
  *                 text you are given.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_diff_print_patch(
 	git_diff_list *diff,
@@ -393,6 +409,8 @@ GIT_EXTERN(int) git_diff_print_patch(
  * When at least one of the blobs being dealt with is binary, the
  * `git_diff_delta` binary attribute will be set to 1 and no call to the
  * hunk_cb nor line_cb will be made.
+ *
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_diff_blobs(
 	git_blob *old_blob,
diff --git a/include/git2/errors.h b/include/git2/errors.h
index ca7f0de6e..2ab1da403 100644
--- a/include/git2/errors.h
+++ b/include/git2/errors.h
@@ -25,6 +25,7 @@ enum {
 	GIT_EEXISTS = -4,
 	GIT_EAMBIGUOUS = -5,
 	GIT_EBUFS = -6,
+	GIT_EUSER = -7,
 
 	GIT_PASSTHROUGH = -30,
 	GIT_REVWALKOVER = -31,
diff --git a/include/git2/notes.h b/include/git2/notes.h
index 19073abd1..b4839bec3 100644
--- a/include/git2/notes.h
+++ b/include/git2/notes.h
@@ -119,19 +119,21 @@ typedef struct {
  *
  * @param repo Repository where to find the notes.
  *
- * @param notes_ref OID reference to read from (optional); defaults to "refs/notes/commits".
+ * @param notes_ref OID reference to read from (optional); defaults to
+ *        "refs/notes/commits".
  *
- * @param note_cb Callback to invoke per found annotation.
+ * @param note_cb Callback to invoke per found annotation.  Return non-zero
+ *        to stop looping.
  *
  * @param payload Extra parameter to callback function.
  *
- * @return 0 or an error code.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_note_foreach(
-		git_repository *repo,
-		const char *notes_ref,
-		int (*note_cb)(git_note_data *note_data, void *payload),
-		void *payload
+	git_repository *repo,
+	const char *notes_ref,
+	int (*note_cb)(git_note_data *note_data, void *payload),
+	void *payload
 );
 
 /** @} */
diff --git a/include/git2/odb.h b/include/git2/odb.h
index dac9e06a9..1f25db463 100644
--- a/include/git2/odb.h
+++ b/include/git2/odb.h
@@ -176,13 +176,14 @@ GIT_EXTERN(int) git_odb_exists(git_odb *db, const git_oid *id);
  * List all objects available in the database
  *
  * The callback will be called for each object available in the
- * database. Note that the objects are likely to be returned in the
- * index order, which would make accessing the objects in that order
- * inefficient.
+ * database. Note that the objects are likely to be returned in the index
+ * order, which would make accessing the objects in that order inefficient.
+ * Return a non-zero value from the callback to stop looping.
  *
  * @param db database to use
  * @param cb the callback to call for each object
  * @param data data to pass to the callback
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_odb_foreach(git_odb *db, int (*cb)(git_oid *oid, void *data), void *data);
 
diff --git a/include/git2/refs.h b/include/git2/refs.h
index b119e90b1..dbd9b7151 100644
--- a/include/git2/refs.h
+++ b/include/git2/refs.h
@@ -268,14 +268,15 @@ GIT_EXTERN(int) git_reference_list(git_strarray *array, git_repository *repo, un
  *
  * The `callback` function will be called for each of the references
  * in the repository, and will receive the name of the reference and
- * the `payload` value passed to this method.
+ * the `payload` value passed to this method.  Returning a non-zero
+ * value from the callback will terminate the iteration.
  *
  * @param repo Repository where to find the refs
  * @param list_flags Filtering flags for the reference
  *		listing.
  * @param callback Function which will be called for every listed ref
  * @param payload Additional data to pass to the callback
- * @return 0 or an error code
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_reference_foreach(git_repository *repo, unsigned int list_flags, int (*callback)(const char *, void *), void *payload);
 
diff --git a/include/git2/remote.h b/include/git2/remote.h
index 5c01949d2..02b93e099 100644
--- a/include/git2/remote.h
+++ b/include/git2/remote.h
@@ -133,9 +133,12 @@ GIT_EXTERN(int) git_remote_connect(git_remote *remote, int direction);
  * The remote (or more exactly its transport) must be connected. The
  * memory belongs to the remote.
  *
+ * If you a return a non-zero value from the callback, this will stop
+ * looping over the refs.
+ *
  * @param refs where to store the refs
  * @param remote the remote
- * @return 0 or an error code
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_remote_ls(git_remote *remote, git_headlist_cb list_cb, void *payload);
 
diff --git a/include/git2/status.h b/include/git2/status.h
index 9e7b5de4a..cc94d7680 100644
--- a/include/git2/status.h
+++ b/include/git2/status.h
@@ -38,11 +38,11 @@ enum {
  *
  * The callback is passed the path of the file, the status and the data
  * pointer passed to this function. If the callback returns something other
- * than 0, this function will return that value.
+ * than 0, this function will stop looping and return GIT_EUSER.
  *
  * @param repo a repository object
  * @param callback the function to call on each file
- * @return 0 on success or the return value of the callback that was non-zero
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 GIT_EXTERN(int) git_status_foreach(
 	git_repository *repo,
diff --git a/src/attr.c b/src/attr.c
index 6fbd005d5..c58a1f045 100644
--- a/src/attr.c
+++ b/src/attr.c
@@ -163,11 +163,14 @@ int git_attr_foreach(
 					continue;
 
 				git_strmap_insert(seen, assign->name, assign, error);
-				if (error >= 0)
-					error = callback(assign->name, assign->value, payload);
-
-				if (error != 0)
+				if (error < 0)
 					goto cleanup;
+
+				error = callback(assign->name, assign->value, payload);
+				if (error) {
+					error = GIT_EUSER;
+					goto cleanup;
+				}
 			}
 		}
 	}
diff --git a/src/config_file.c b/src/config_file.c
index 7ced1e5ba..80c63d2a3 100644
--- a/src/config_file.c
+++ b/src/config_file.c
@@ -218,8 +218,10 @@ static int file_foreach(
 				continue;
 
 			/* abort iterator on non-zero return value */
-			if ((result = fn(key, var->value, data)) != 0)
+			if (fn(key, var->value, data)) {
+				result = GIT_EUSER;
 				goto cleanup;
+			}
 		}
 	);
 
diff --git a/src/diff_output.c b/src/diff_output.c
index f6650b345..9f8779787 100644
--- a/src/diff_output.c
+++ b/src/diff_output.c
@@ -23,6 +23,7 @@ typedef struct {
 	unsigned int index;
 	git_diff_delta *delta;
 	git_diff_range range;
+	int error;
 } diff_output_info;
 
 static int read_next_int(const char **str, int *value)
@@ -49,25 +50,24 @@ static int diff_output_cb(void *priv, mmbuffer_t *bufs, int len)
 
 		/* expect something of the form "@@ -%d[,%d] +%d[,%d] @@" */
 		if (*scan != '@')
-			return -1;
+			info->error = -1;
+		else if (read_next_int(&scan, &range.old_start) < 0)
+			info->error = -1;
+		else if (*scan == ',' && read_next_int(&scan, &range.old_lines) < 0)
+			info->error = -1;
+		else if (read_next_int(&scan, &range.new_start) < 0)
+			info->error = -1;
+		else if (*scan == ',' && read_next_int(&scan, &range.new_lines) < 0)
+			info->error = -1;
+		else if (range.old_start < 0 || range.new_start < 0)
+			info->error = -1;
+		else {
+			memcpy(&info->range, &range, sizeof(git_diff_range));
 
-		if (read_next_int(&scan, &range.old_start) < 0)
-			return -1;
-		if (*scan == ',' && read_next_int(&scan, &range.old_lines) < 0)
-			return -1;
-
-		if (read_next_int(&scan, &range.new_start) < 0)
-			return -1;
-		if (*scan == ',' && read_next_int(&scan, &range.new_lines) < 0)
-			return -1;
-
-		if (range.old_start < 0 || range.new_start < 0)
-			return -1;
-
-		memcpy(&info->range, &range, sizeof(git_diff_range));
-
-		return info->hunk_cb(
-			info->cb_data, info->delta, &range, bufs[0].ptr, bufs[0].size);
+			if (info->hunk_cb(
+					info->cb_data, info->delta, &range, bufs[0].ptr, bufs[0].size))
+				info->error = GIT_EUSER;
+		}
 	}
 
 	if ((len == 2 || len == 3) && info->line_cb) {
@@ -80,23 +80,24 @@ static int diff_output_cb(void *priv, mmbuffer_t *bufs, int len)
 			GIT_DIFF_LINE_CONTEXT;
 
 		if (info->line_cb(
-			info->cb_data, info->delta, &info->range, origin, bufs[1].ptr, bufs[1].size) < 0)
-			return -1;
+				info->cb_data, info->delta, &info->range, origin, bufs[1].ptr, bufs[1].size))
+			info->error = GIT_EUSER;
 
 		/* This should only happen if we are adding a line that does not
 		 * have a newline at the end and the old code did.  In that case,
 		 * we have a ADD with a DEL_EOFNL as a pair.
 		 */
-		if (len == 3) {
+		else if (len == 3) {
 			origin = (origin == GIT_DIFF_LINE_ADDITION) ?
 				GIT_DIFF_LINE_DEL_EOFNL : GIT_DIFF_LINE_ADD_EOFNL;
 
-			return info->line_cb(
-				info->cb_data, info->delta, &info->range, origin, bufs[2].ptr, bufs[2].size);
+			if (info->line_cb(
+					info->cb_data, info->delta, &info->range, origin, bufs[2].ptr, bufs[2].size))
+				info->error = GIT_EUSER;
 		}
 	}
 
-	return 0;
+	return info->error;
 }
 
 #define BINARY_DIFF_FLAGS (GIT_DIFF_FILE_BINARY|GIT_DIFF_FILE_NOT_BINARY)
@@ -318,6 +319,7 @@ int git_diff_foreach(
 	xdemitconf_t xdiff_config;
 	xdemitcb_t   xdiff_callback;
 
+	memset(&info, 0, sizeof(info));
 	info.diff    = diff;
 	info.cb_data = data;
 	info.hunk_cb = hunk_cb;
@@ -422,11 +424,11 @@ int git_diff_foreach(
 		 * diffs to tell if a file has really been changed.
 		 */
 
-		if (file_cb != NULL) {
-			error = file_cb(
-				data, delta, (float)info.index / diff->deltas.length);
-			if (error < 0)
-				goto cleanup;
+		if (file_cb != NULL &&
+			file_cb(data, delta, (float)info.index / diff->deltas.length))
+		{
+			error = GIT_EUSER;
+			goto cleanup;
 		}
 
 		/* don't do hunk and line diffs if file is binary */
@@ -451,6 +453,7 @@ int git_diff_foreach(
 
 		xdl_diff(&old_xdiff_data, &new_xdiff_data,
 			&xdiff_params, &xdiff_config, &xdiff_callback);
+		error = info.error;
 
 cleanup:
 		release_content(&delta->old_file, &old_data, old_blob);
@@ -524,7 +527,11 @@ static int print_compact(void *data, git_diff_delta *delta, float progress)
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-	return pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 int git_diff_print_compact(
@@ -586,7 +593,6 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	const char *oldpath = delta->old_file.path;
 	const char *newpfx = pi->diff->opts.new_prefix;
 	const char *newpath = delta->new_file.path;
-	int result;
 
 	GIT_UNUSED(progress);
 
@@ -619,9 +625,8 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-    result = pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
-    if (result < 0)
-        return result;
+    if (pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_FILE_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
 
     if (delta->binary != 1)
         return 0;
@@ -633,7 +638,11 @@ static int print_patch_file(void *data, git_diff_delta *delta, float progress)
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-	return pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_BINARY, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, delta, NULL, GIT_DIFF_LINE_BINARY,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 static int print_patch_hunk(
@@ -649,7 +658,11 @@ static int print_patch_hunk(
 	if (git_buf_printf(pi->buf, "%.*s", (int)header_len, header) < 0)
 		return -1;
 
-	return pi->print_cb(pi->cb_data, d, r, GIT_DIFF_LINE_HUNK_HDR, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, d, r, GIT_DIFF_LINE_HUNK_HDR,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 static int print_patch_line(
@@ -674,7 +687,11 @@ static int print_patch_line(
 	if (git_buf_oom(pi->buf))
 		return -1;
 
-	return pi->print_cb(pi->cb_data, delta, range, line_origin, git_buf_cstr(pi->buf), git_buf_len(pi->buf));
+	if (pi->print_cb(pi->cb_data, delta, range, line_origin,
+			git_buf_cstr(pi->buf), git_buf_len(pi->buf)))
+		return GIT_EUSER;
+
+	return 0;
 }
 
 int git_diff_print_patch(
@@ -763,11 +780,8 @@ int git_diff_blobs(
 	if (file_is_binary_by_content(&delta, &old_map, &new_map) < 0)
 		return -1;
 
-	if (file_cb != NULL) {
-		int error = file_cb(cb_data, &delta, 1);
-		if (error < 0)
-			return error;
-	}
+	if (file_cb != NULL && file_cb(cb_data, &delta, 1))
+		return GIT_EUSER;
 
 	/* don't do hunk and line diffs if the two blobs are identical */
 	if (delta.status == GIT_DELTA_UNMODIFIED)
@@ -777,6 +791,7 @@ int git_diff_blobs(
 	if (delta.binary == 1)
 		return 0;
 
+	memset(&info, 0, sizeof(info));
 	info.diff    = NULL;
 	info.delta   = &delta;
 	info.cb_data = cb_data;
@@ -790,5 +805,5 @@ int git_diff_blobs(
 
 	xdl_diff(&old_data, &new_data, &xdiff_params, &xdiff_config, &xdiff_callback);
 
-	return 0;
+	return info.error;
 }
diff --git a/src/notes.c b/src/notes.c
index 7813e9985..212413a5a 100644
--- a/src/notes.c
+++ b/src/notes.c
@@ -522,13 +522,13 @@ static int process_entry_path(
 	int (*note_cb)(git_note_data *note_data, void *payload),
 	void *payload)
 {
-	int i = 0, j = 0, error = -1, len;
+	int i = 0, j = 0, error, len;
 	git_buf buf = GIT_BUF_INIT;
 	git_note_data note_data;
 
-	if (git_buf_puts(&buf, entry_path) < 0)
+	if ((error = git_buf_puts(&buf, entry_path)) < 0)
 		goto cleanup;
-	
+
 	len = git_buf_len(&buf);
 
 	while (i < len) {
@@ -536,10 +536,9 @@ static int process_entry_path(
 			i++;
 			continue;
 		}
-		
+
 		if (git__fromhex(buf.ptr[i]) < 0) {
 			/* This is not a note entry */
-			error = 0;
 			goto cleanup;
 		}
 
@@ -555,16 +554,17 @@ static int process_entry_path(
 
 	if (j != GIT_OID_HEXSZ) {
 		/* This is not a note entry */
-		error = 0;
 		goto cleanup;
 	}
 
-	if (git_oid_fromstr(&note_data.annotated_object_oid, buf.ptr) < 0)
-		return -1;
+	if ((error = git_oid_fromstr(
+			&note_data.annotated_object_oid, buf.ptr)) < 0)
+		goto cleanup;
 
 	git_oid_cpy(&note_data.blob_oid, note_oid);
 
-	error = note_cb(&note_data, payload);
+	if (note_cb(&note_data, payload))
+		error = GIT_EUSER;
 
 cleanup:
 	git_buf_free(&buf);
@@ -577,34 +577,27 @@ int git_note_foreach(
 	int (*note_cb)(git_note_data *note_data, void *payload),
 	void *payload)
 {
-	int error = -1;
+	int error;
 	git_iterator *iter = NULL;
 	git_tree *tree = NULL;
 	git_commit *commit = NULL;
 	const git_index_entry *item;
 
-	if ((error = retrieve_note_tree_and_commit(&tree, &commit, repo, &notes_ref)) < 0)
-		goto cleanup;
+	if (!(error = retrieve_note_tree_and_commit(
+			&tree, &commit, repo, &notes_ref)) &&
+		!(error = git_iterator_for_tree(&iter, repo, tree)))
+		error = git_iterator_current(iter, &item);
 
-	if (git_iterator_for_tree(&iter, repo, tree) < 0)
-		goto cleanup;
+	while (!error && item) {
+		error = process_entry_path(item->path, &item->oid, note_cb, payload);
 
-	if (git_iterator_current(iter, &item) < 0)
-		goto cleanup;
-
-	while (item) {
-		if (process_entry_path(item->path, &item->oid, note_cb, payload) < 0)
-			goto cleanup;
-
-		if (git_iterator_advance(iter, &item) < 0)
-			goto cleanup;
+		if (!error)
+			error = git_iterator_advance(iter, &item);
 	}
 
-	error = 0;
-
-cleanup:
 	git_iterator_free(iter);
 	git_tree_free(tree);
 	git_commit_free(commit);
+
 	return error;
 }
diff --git a/src/odb.c b/src/odb.c
index 493c8292a..db2f03c9e 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -609,9 +609,12 @@ int git_odb_foreach(git_odb *db, int (*cb)(git_oid *oid, void *data), void *data
 {
 	unsigned int i;
 	backend_internal *internal;
+
 	git_vector_foreach(&db->backends, i, internal) {
 		git_odb_backend *b = internal->backend;
-		b->foreach(b, cb, data);
+		int error = b->foreach(b, cb, data);
+		if (error < 0)
+			return error;
 	}
 
 	return 0;
diff --git a/src/odb_loose.c b/src/odb_loose.c
index 2197a4264..ccb899e8c 100644
--- a/src/odb_loose.c
+++ b/src/odb_loose.c
@@ -680,6 +680,7 @@ struct foreach_state {
 	size_t dir_len;
 	int (*cb)(git_oid *oid, void *data);
 	void *data;
+	int cb_error;
 };
 
 GIT_INLINE(int) filename_to_oid(git_oid *oid, const char *ptr)
@@ -718,8 +719,10 @@ static int foreach_object_dir_cb(void *_state, git_buf *path)
 	if (filename_to_oid(&oid, path->ptr + state->dir_len) < 0)
 		return 0;
 
-	if (state->cb(&oid, state->data) < 0)
+	if (state->cb(&oid, state->data)) {
+		state->cb_error = GIT_EUSER;
 		return -1;
+	}
 
 	return 0;
 }
@@ -728,10 +731,7 @@ static int foreach_cb(void *_state, git_buf *path)
 {
 	struct foreach_state *state = (struct foreach_state *) _state;
 
-	if (git_path_direach(path, foreach_object_dir_cb, state) < 0)
-		return -1;
-
-	return 0;
+	return git_path_direach(path, foreach_object_dir_cb, state);
 }
 
 static int loose_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *oid, void *data), void *data)
@@ -749,14 +749,16 @@ static int loose_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *
 	git_buf_sets(&buf, objects_dir);
 	git_path_to_dir(&buf);
 
+	memset(&state, 0, sizeof(state));
 	state.cb = cb;
 	state.data = data;
 	state.dir_len = git_buf_len(&buf);
 
 	error = git_path_direach(&buf, foreach_cb, &state);
+
 	git_buf_free(&buf);
 
-	return error;
+	return state.cb_error ? state.cb_error : error;
 }
 
 static int loose_backend__stream_fwrite(git_oid *oid, git_odb_stream *_stream)
diff --git a/src/odb_pack.c b/src/odb_pack.c
index 4b860e864..176be5f01 100644
--- a/src/odb_pack.c
+++ b/src/odb_pack.c
@@ -422,6 +422,7 @@ static int pack_backend__exists(git_odb_backend *backend, const git_oid *oid)
 
 static int pack_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *oid, void *data), void *data)
 {
+	int error;
 	struct git_pack_file *p;
 	struct pack_backend *backend;
 	unsigned int i;
@@ -430,12 +431,14 @@ static int pack_backend__foreach(git_odb_backend *_backend, int (*cb)(git_oid *o
 	backend = (struct pack_backend *)_backend;
 
 	/* Make sure we know about the packfiles */
-	if (packfile_refresh_all(backend) < 0)
-		return -1;
+	if ((error = packfile_refresh_all(backend)) < 0)
+		return error;
 
 	git_vector_foreach(&backend->packs, i, p) {
-		git_pack_foreach_entry(p, cb, &data);
+		if ((error = git_pack_foreach_entry(p, cb, &data)) < 0)
+			return error;
 	}
+
 	return 0;
 }
 
diff --git a/src/pack.c b/src/pack.c
index 1d88eaa7d..acdb40d35 100644
--- a/src/pack.c
+++ b/src/pack.c
@@ -687,10 +687,9 @@ static git_off_t nth_packed_object_offset(const struct git_pack_file *p, uint32_
 }
 
 int git_pack_foreach_entry(
-		struct git_pack_file *p,
-		int (*cb)(git_oid *oid, void *data),
-		void *data)
-
+	struct git_pack_file *p,
+	int (*cb)(git_oid *oid, void *data),
+	void *data)
 {
 	const unsigned char *index = p->index_map.data, *current;
 	unsigned stride;
@@ -722,7 +721,9 @@ int git_pack_foreach_entry(
 
 	current = index;
 	for (i = 0; i < p->num_objects; i++) {
-		cb((git_oid *)current, data);
+		if (cb((git_oid *)current, data))
+			return GIT_EUSER;
+
 		current += stride;
 	}
 
diff --git a/src/path.h b/src/path.h
index d68393b3d..d611428c1 100644
--- a/src/path.h
+++ b/src/path.h
@@ -217,6 +217,7 @@ extern int git_path_apply_relative(git_buf *target, const char *relpath);
  *		the input state and the second arg is pathbuf. The function
  *		may modify the pathbuf, but only by appending new text.
  * @param state to pass to fn as the first arg.
+ * @return 0 on success, GIT_EUSER on non-zero callback, or error code
  */
 extern int git_path_direach(
 	git_buf *pathbuf,
diff --git a/src/refs.c b/src/refs.c
index b3c140bec..723695cd6 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -501,6 +501,7 @@ struct dirent_list_data {
 
 	int (*callback)(const char *, void *);
 	void *callback_payload;
+	int callback_error;
 };
 
 static int _dirent_loose_listall(void *_data, git_buf *full_path)
@@ -521,7 +522,10 @@ static int _dirent_loose_listall(void *_data, git_buf *full_path)
 			return 0; /* we are filtering out this reference */
 	}
 
-	return data->callback(file_path, data->callback_payload);
+	if (data->callback(file_path, data->callback_payload))
+		data->callback_error = GIT_EUSER;
+
+	return data->callback_error;
 }
 
 static int _dirent_loose_load(void *data, git_buf *full_path)
@@ -844,15 +848,17 @@ static int reference_path_available(
 	const char *ref,
 	const char* old_ref)
 {
+	int error;
 	struct reference_available_t data;
 
 	data.new_ref = ref;
 	data.old_ref = old_ref;
 	data.available = 1;
 
-	if (git_reference_foreach(repo, GIT_REF_LISTALL,
-		_reference_available_cb, (void *)&data) < 0)
-		return -1;
+	error = git_reference_foreach(
+		repo, GIT_REF_LISTALL, _reference_available_cb, (void *)&data);
+	if (error < 0)
+		return error;
 
 	if (!data.available) {
 		giterr_set(GITERR_REFERENCE,
@@ -1487,8 +1493,8 @@ int git_reference_foreach(
 			return -1;
 
 		git_strmap_foreach(repo->references.packfile, ref_name, ref, {
-			if (callback(ref_name, payload) < 0)
-				return 0;
+			if (callback(ref_name, payload))
+				return GIT_EUSER;
 		});
 	}
 
@@ -1500,14 +1506,16 @@ int git_reference_foreach(
 	data.repo = repo;
 	data.callback = callback;
 	data.callback_payload = payload;
+	data.callback_error = 0;
 
 	if (git_buf_joinpath(&refs_path, repo->path_repository, GIT_REFS_DIR) < 0)
 		return -1;
 
 	result = git_path_direach(&refs_path, _dirent_loose_listall, &data);
+
 	git_buf_free(&refs_path);
 
-	return result;
+	return data.callback_error ? GIT_EUSER : result;
 }
 
 static int cb__reflist_add(const char *ref, void *data)
diff --git a/src/status.c b/src/status.c
index d78237689..618f60fd0 100644
--- a/src/status.c
+++ b/src/status.c
@@ -114,7 +114,8 @@ int git_status_foreach_ext(
 	if (show == GIT_STATUS_SHOW_INDEX_THEN_WORKDIR) {
 		for (i = 0; !err && i < idx2head->deltas.length; i++) {
 			i2h = GIT_VECTOR_GET(&idx2head->deltas, i);
-			err = cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata);
+			if (cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata))
+				err = GIT_EUSER;
 		}
 		git_diff_list_free(idx2head);
 		idx2head = NULL;
@@ -130,14 +131,17 @@ int git_status_foreach_ext(
 		cmp = !w2i ? -1 : !i2h ? 1 : strcmp(i2h->old_file.path, w2i->old_file.path);
 
 		if (cmp < 0) {
-			err = cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata);
+			if (cb(i2h->old_file.path, index_delta2status(i2h->status), cbdata))
+				err = GIT_EUSER;
 			i++;
 		} else if (cmp > 0) {
-			err = cb(w2i->old_file.path, workdir_delta2status(w2i->status), cbdata);
+			if (cb(w2i->old_file.path, workdir_delta2status(w2i->status), cbdata))
+				err = GIT_EUSER;
 			j++;
 		} else {
-			err = cb(i2h->old_file.path, index_delta2status(i2h->status) |
-					 workdir_delta2status(w2i->status), cbdata);
+			if (cb(i2h->old_file.path, index_delta2status(i2h->status) |
+				   workdir_delta2status(w2i->status), cbdata))
+				err = GIT_EUSER;
 			i++; j++;
 		}
 	}
@@ -146,6 +150,7 @@ cleanup:
 	git_tree_free(head);
 	git_diff_list_free(idx2head);
 	git_diff_list_free(wd2idx);
+
 	return err;
 }
 
@@ -166,9 +171,10 @@ int git_status_foreach(
 }
 
 struct status_file_info {
+	char *expected;
 	unsigned int count;
 	unsigned int status;
-	char *expected;
+	int ambiguous;
 };
 
 static int get_one_status(const char *path, unsigned int status, void *data)
@@ -183,6 +189,7 @@ static int get_one_status(const char *path, unsigned int status, void *data)
 		p_fnmatch(sfi->expected, path, 0) != 0)) {
 		giterr_set(GITERR_INVALID,
 			"Ambiguous path '%s' given to git_status_file", sfi->expected);
+		sfi->ambiguous = true;
 		return GIT_EAMBIGUOUS;
 	}
 
@@ -215,6 +222,9 @@ int git_status_file(
 
 	error = git_status_foreach_ext(repo, &opts, get_one_status, &sfi);
 
+	if (error < 0 && sfi.ambiguous)
+		error = GIT_EAMBIGUOUS;
+
 	if (!error && !sfi.count) {
 		giterr_set(GITERR_INVALID,
 			"Attempt to get status of nonexistent file '%s'", path);
diff --git a/src/transports/git.c b/src/transports/git.c
index 45f571f20..0d0ec7821 100644
--- a/src/transports/git.c
+++ b/src/transports/git.c
@@ -239,10 +239,8 @@ static int git_ls(git_transport *transport, git_headlist_cb list_cb, void *opaqu
 
 		pkt = (git_pkt_ref *)p;
 
-		if (list_cb(&pkt->head, opaque) < 0) {
-			giterr_set(GITERR_NET, "User callback returned error");
-			return -1;
-		}
+		if (list_cb(&pkt->head, opaque))
+			return GIT_EUSER;
 	}
 
 	return 0;
diff --git a/src/transports/http.c b/src/transports/http.c
index f25d639f3..993070aac 100644
--- a/src/transports/http.c
+++ b/src/transports/http.c
@@ -324,10 +324,8 @@ static int http_ls(git_transport *transport, git_headlist_cb list_cb, void *opaq
 		if (p->type != GIT_PKT_REF)
 			continue;
 
-		if (list_cb(&p->head, opaque) < 0) {
-			giterr_set(GITERR_NET, "The user callback returned error");
-			return -1;
-		}
+		if (list_cb(&p->head, opaque))
+			return GIT_EUSER;
 	}
 
 	return 0;
diff --git a/src/transports/local.c b/src/transports/local.c
index 0e1ae3752..ccbfb0492 100644
--- a/src/transports/local.c
+++ b/src/transports/local.c
@@ -126,8 +126,8 @@ static int local_ls(git_transport *transport, git_headlist_cb list_cb, void *pay
 	assert(transport && transport->connected);
 
 	git_vector_foreach(refs, i, h) {
-		if (list_cb(h, payload) < 0)
-			return -1;
+		if (list_cb(h, payload))
+			return GIT_EUSER;
 	}
 
 	return 0;
diff --git a/tests-clar/attr/repo.c b/tests-clar/attr/repo.c
index c37ff544a..4a317e4f3 100644
--- a/tests-clar/attr/repo.c
+++ b/tests-clar/attr/repo.c
@@ -113,6 +113,22 @@ static int count_attrs(
 	return 0;
 }
 
+static int cancel_iteration(
+	const char *name,
+	const char *value,
+	void *payload)
+{
+	GIT_UNUSED(name);
+	GIT_UNUSED(value);
+
+	*((int *)payload) -= 1;
+
+	if (*((int *)payload) < 0)
+		return -1;
+
+	return 0;
+}
+
 void test_attr_repo__foreach(void)
 {
 	int count;
@@ -131,6 +147,12 @@ void test_attr_repo__foreach(void)
 	cl_git_pass(git_attr_foreach(g_repo, 0, "sub/subdir_test2.txt",
 		&count_attrs, &count));
 	cl_assert(count == 6); /* repoattr, rootattr, subattr, reposub, negattr, another */
+
+	count = 2;
+	cl_assert_equal_i(
+		GIT_EUSER, git_attr_foreach(
+			g_repo, 0, "sub/subdir_test1", &cancel_iteration, &count)
+	);
 }
 
 void test_attr_repo__manpage_example(void)
diff --git a/tests-clar/config/read.c b/tests-clar/config/read.c
index a8504da02..574ff8196 100644
--- a/tests-clar/config/read.c
+++ b/tests-clar/config/read.c
@@ -226,7 +226,7 @@ void test_config_read__foreach(void)
 
 	count = 3;
 	cl_git_fail(ret = git_config_foreach(cfg, cfg_callback_countdown, &count));
-	cl_assert_equal_i(-100, ret);
+	cl_assert_equal_i(GIT_EUSER, ret);
 
 	git_config_free(cfg);
 }
diff --git a/tests-clar/diff/index.c b/tests-clar/diff/index.c
index 171815df5..89e65e3b7 100644
--- a/tests-clar/diff/index.c
+++ b/tests-clar/diff/index.c
@@ -90,3 +90,53 @@ void test_diff_index__0(void)
 	git_tree_free(a);
 	git_tree_free(b);
 }
+
+static int diff_stop_after_2_files(
+	void *cb_data,
+	git_diff_delta *delta,
+	float progress)
+{
+	diff_expects *e = cb_data;
+
+	GIT_UNUSED(progress);
+	GIT_UNUSED(delta);
+
+	e->files++;
+
+	return (e->files == 2);
+}
+
+void test_diff_index__1(void)
+{
+	/* grabbed a couple of commit oids from the history of the attr repo */
+	const char *a_commit = "26a125ee1bf"; /* the current HEAD */
+	const char *b_commit = "0017bd4ab1ec3"; /* the start */
+	git_tree *a = resolve_commit_oid_to_tree(g_repo, a_commit);
+	git_tree *b = resolve_commit_oid_to_tree(g_repo, b_commit);
+	git_diff_options opts = {0};
+	git_diff_list *diff = NULL;
+	diff_expects exp;
+
+	cl_assert(a);
+	cl_assert(b);
+
+	opts.context_lines = 1;
+	opts.interhunk_lines = 1;
+
+	memset(&exp, 0, sizeof(exp));
+
+	cl_git_pass(git_diff_index_to_tree(g_repo, &opts, a, &diff));
+
+	cl_assert_equal_i(
+		GIT_EUSER,
+		git_diff_foreach(diff, &exp, diff_stop_after_2_files, NULL, NULL)
+	);
+
+	cl_assert(exp.files == 2);
+
+	git_diff_list_free(diff);
+	diff = NULL;
+
+	git_tree_free(a);
+	git_tree_free(b);
+}
diff --git a/tests-clar/notes/notes.c b/tests-clar/notes/notes.c
index e1387782e..dfd7f5231 100644
--- a/tests-clar/notes/notes.c
+++ b/tests-clar/notes/notes.c
@@ -95,11 +95,39 @@ void test_notes_notes__can_retrieve_a_list_of_notes_for_a_given_namespace(void)
 	create_note(&note_oid3, "refs/notes/i-can-see-dead-notes", "9fd738e8f7967c078dceed8190330fc8648ee56a", "I decorate 9fd7 and 4a20\n");
 	create_note(&note_oid4, "refs/notes/i-can-see-dead-notes", "4a202b346bb0fb0db7eff3cffeb3c70babbd2045", "I decorate 9fd7 and 4a20\n");
 
-	cl_git_pass(git_note_foreach(_repo, "refs/notes/i-can-see-dead-notes", note_list_cb, &retrieved_notes));
+	cl_git_pass(git_note_foreach
+(_repo, "refs/notes/i-can-see-dead-notes", note_list_cb, &retrieved_notes));
 
 	cl_assert_equal_i(4, retrieved_notes);
 }
 
+static int note_cancel_cb(git_note_data *note_data, void *payload)
+{
+	unsigned int *count = (unsigned int *)payload;
+
+	GIT_UNUSED(note_data);
+
+	(*count)++;
+
+	return (*count > 2);
+}
+
+void test_notes_notes__can_cancel_foreach(void)
+{
+	git_oid note_oid1, note_oid2, note_oid3, note_oid4;
+	unsigned int retrieved_notes = 0;
+
+	create_note(&note_oid1, "refs/notes/i-can-see-dead-notes", "a65fedf39aefe402d3bb6e24df4d4f5fe4547750", "I decorate a65f\n");
+	create_note(&note_oid2, "refs/notes/i-can-see-dead-notes", "c47800c7266a2be04c571c04d5a6614691ea99bd", "I decorate c478\n");
+	create_note(&note_oid3, "refs/notes/i-can-see-dead-notes", "9fd738e8f7967c078dceed8190330fc8648ee56a", "I decorate 9fd7 and 4a20\n");
+	create_note(&note_oid4, "refs/notes/i-can-see-dead-notes", "4a202b346bb0fb0db7eff3cffeb3c70babbd2045", "I decorate 9fd7 and 4a20\n");
+
+	cl_assert_equal_i(
+		GIT_EUSER,
+		git_note_foreach(_repo, "refs/notes/i-can-see-dead-notes",
+			note_cancel_cb, &retrieved_notes));
+}
+
 void test_notes_notes__retrieving_a_list_of_notes_for_an_unknown_namespace_returns_ENOTFOUND(void)
 {
 	int error;
diff --git a/tests-clar/odb/foreach.c b/tests-clar/odb/foreach.c
index 525c70c09..e025fa210 100644
--- a/tests-clar/odb/foreach.c
+++ b/tests-clar/odb/foreach.c
@@ -31,6 +31,24 @@ static int foreach_cb(git_oid *oid, void *data)
 
 void test_odb_foreach__foreach(void)
 {
+	nobj = 0;
 	cl_git_pass(git_odb_foreach(_odb, foreach_cb, NULL));
 	cl_assert(nobj == 1683);
 }
+
+static int foreach_stop_cb(git_oid *oid, void *data)
+{
+	GIT_UNUSED(data);
+	GIT_UNUSED(oid);
+
+	nobj++;
+
+	return (nobj == 1000);
+}
+
+void test_odb_foreach__interrupt_foreach(void)
+{
+	nobj = 0;
+	cl_assert_equal_i(GIT_EUSER, git_odb_foreach(_odb, foreach_stop_cb, NULL));
+	cl_assert(nobj == 1000);
+}
diff --git a/tests-clar/refs/branches/foreach.c b/tests-clar/refs/branches/foreach.c
index b6e973799..8b39b7dc8 100644
--- a/tests-clar/refs/branches/foreach.c
+++ b/tests-clar/refs/branches/foreach.c
@@ -126,3 +126,28 @@ void test_refs_branches_foreach__retrieve_remote_symbolic_HEAD_when_present(void
 	assert_branch_has_been_found(exp, "nulltoken/HEAD");
 	assert_branch_has_been_found(exp, "nulltoken/HEAD");
 }
+
+static int branch_list_interrupt_cb(
+	const char *branch_name, git_branch_t branch_type, void *payload)
+{
+	int *count;
+
+	GIT_UNUSED(branch_type);
+	GIT_UNUSED(branch_name);
+
+	count = (int *)payload;
+	(*count)++;
+
+	return (*count == 5);
+}
+
+void test_refs_branches_foreach__can_cancel(void)
+{
+	int count = 0;
+
+	cl_assert_equal_i(GIT_EUSER,
+		git_branch_foreach(repo, GIT_BRANCH_LOCAL | GIT_BRANCH_REMOTE,
+			branch_list_interrupt_cb, &count));
+
+	cl_assert_equal_i(5, count);
+}
diff --git a/tests-clar/refs/foreachglob.c b/tests-clar/refs/foreachglob.c
index d1412a94b..7d514d461 100644
--- a/tests-clar/refs/foreachglob.c
+++ b/tests-clar/refs/foreachglob.c
@@ -68,3 +68,25 @@ void test_refs_foreachglob__retrieve_partially_named_references(void)
 
 	assert_retrieval("*test*", GIT_REF_LISTALL, 4);
 }
+
+
+static int interrupt_cb(const char *reference_name, void *payload)
+{
+	int *count = (int *)payload;
+
+	GIT_UNUSED(reference_name);
+
+	(*count)++;
+
+	return (*count == 11);
+}
+
+void test_refs_foreachglob__can_cancel(void)
+{
+	int count = 0;
+
+	cl_assert_equal_i(GIT_EUSER, git_reference_foreach_glob(
+		repo, "*", GIT_REF_LISTALL, interrupt_cb, &count) );
+
+	cl_assert_equal_i(11, count);
+}
diff --git a/tests-clar/status/worktree.c b/tests-clar/status/worktree.c
index d84cb77ed..bfd257a3b 100644
--- a/tests-clar/status/worktree.c
+++ b/tests-clar/status/worktree.c
@@ -530,7 +530,7 @@ void test_status_worktree__bracket_in_filename(void)
 
 	cl_git_pass(git_repository_init(&repo, "with_bracket", 0));
 	cl_git_mkfile("with_bracket/" FILE_WITH_BRACKET, "I have a bracket in my name\n");
-	
+
 	/* file is new to working directory */
 
 	memset(&result, 0, sizeof(result));
@@ -578,7 +578,7 @@ void test_status_worktree__bracket_in_filename(void)
 
 	cl_git_pass(git_status_file(&status_flags, repo, FILE_WITH_BRACKET));
 	cl_assert(status_flags == GIT_STATUS_INDEX_NEW);
-	
+
 	/* Create file without bracket */
 
 	cl_git_mkfile("with_bracket/" FILE_WITHOUT_BRACKET, "I have no bracket in my name!\n");
@@ -591,7 +591,7 @@ void test_status_worktree__bracket_in_filename(void)
 
 	error = git_status_file(&status_flags, repo, FILE_WITH_BRACKET);
 	cl_git_fail(error);
-	cl_assert(error == GIT_EAMBIGUOUS);
+	cl_assert_equal_i(GIT_EAMBIGUOUS, error);
 
 	git_index_free(index);
 	git_repository_free(repo);
@@ -769,6 +769,31 @@ void test_status_worktree__disable_pathspec_match(void)
 	cl_git_pass(
 		git_status_foreach_ext(repo, &opts, cb_status__expected_path, NULL)
 	);
-	
+
 	git_repository_free(repo);
 }
+
+
+static int cb_status__interrupt(const char *p, unsigned int s, void *payload)
+{
+	volatile int *count = (int *)payload;
+
+	GIT_UNUSED(p);
+	GIT_UNUSED(s);
+
+	(*count)++;
+
+	return (*count == 8);
+}
+
+void test_status_worktree__interruptable_foreach(void)
+{
+	int count = 0;
+	git_repository *repo = cl_git_sandbox_init("status");
+
+	cl_assert_equal_i(
+		GIT_EUSER, git_status_foreach(repo, cb_status__interrupt, &count)
+	);
+
+	cl_assert_equal_i(8, count);
+}