diff --git a/commit.h b/commit.h
index 5cc1e7ec9e..9f189cb054 100644
--- a/commit.h
+++ b/commit.h
@@ -254,7 +254,6 @@ extern int for_each_commit_graft(each_commit_graft_fn, void *);
 extern int is_repository_shallow(void);
 extern struct commit_list *get_shallow_commits(struct object_array *heads,
 		int depth, int shallow_flag, int not_shallow_flag);
-extern void check_shallow_file_for_update(void);
 extern void set_alternate_shallow_file(const char *path, int override);
 extern int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 				 const struct sha1_array *extra);
diff --git a/shallow.c b/shallow.c
index cdd0775146..04ea816e0e 100644
--- a/shallow.c
+++ b/shallow.c
@@ -137,7 +137,7 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
 	return result;
 }
 
-void check_shallow_file_for_update(void)
+static void check_shallow_file_for_update(void)
 {
 	if (is_shallow == -1)
 		die("BUG: shallow must be initialized by now");