diff --git a/builtin/apply.c b/builtin/apply.c
index 9c5724eacc..bc924ab2d0 100644
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -3847,9 +3847,10 @@ static void add_index_file(const char *path, unsigned mode, void *buf, unsigned
 	ce->ce_flags = create_ce_flags(0);
 	ce->ce_namelen = namelen;
 	if (S_ISGITLINK(mode)) {
-		const char *s = buf;
+		const char *s;
 
-		if (get_sha1_hex(s + strlen("Subproject commit "), ce->sha1))
+		if (!skip_prefix(buf, "Subproject commit ", &s) ||
+		    get_sha1_hex(s, ce->sha1))
 			die(_("corrupt patch for submodule %s"), path);
 	} else {
 		if (!cached) {