diff --git a/builtin/commit.c b/builtin/commit.c
index b0fe7847d3..70f5935f1b 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -315,8 +315,8 @@ static void refresh_cache_or_die(int refresh_flags)
 		die_resolve_conflict("commit");
 }
 
-static char *prepare_index(int argc, const char **argv, const char *prefix,
-			   const struct commit *current_head, int is_status)
+static const char *prepare_index(int argc, const char **argv, const char *prefix,
+				 const struct commit *current_head, int is_status)
 {
 	struct string_list partial;
 	struct pathspec pathspec;