diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index a4615587fd..736f666f64 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c

@@ -106,7 +106,7 @@ static int handle_line(char *line, struct merge_parents *merge_parents)
 	int i, len = strlen(line);
 	struct origin_data *origin_data;
 	char *src;
-	const char *origin;
+	const char *origin, *tag_name;
 	struct src_data *src_data;
 	struct string_list_item *item;
 	int pulling_head = 0;

@@ -162,14 +162,13 @@ static int handle_line(char *line, struct merge_parents *merge_parents)
 	if (pulling_head) {
 		origin = src;
 		src_data->head_status |= 1;
-	} else if (starts_with(line, "branch ")) {
+	} else if (skip_prefix(line, "branch ", &origin)) {
 		origin_data->is_local_branch = 1;
-		origin = line + 7;
 		string_list_append(&src_data->branch, origin);
 		src_data->head_status |= 2;
-	} else if (starts_with(line, "tag ")) {
+	} else if (skip_prefix(line, "tag ", &tag_name)) {
 		origin = line;
-		string_list_append(&src_data->tag, origin + 4);
+		string_list_append(&src_data->tag, tag_name);
 		src_data->head_status |= 2;