diff --git a/sequencer.c b/sequencer.c
index bde5f047b0..0a80c58d11 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -281,8 +281,12 @@ static int fast_forward_to(const unsigned char *to, const unsigned char *from,
 		exit(1); /* the callee should have complained already */
 	ref_lock = lock_any_ref_for_update("HEAD", unborn ? null_sha1 : from,
 					   0, NULL);
+	if (!ref_lock)
+		return error(_("Failed to lock HEAD during fast_forward_to"));
+
 	strbuf_addf(&sb, "%s: fast-forward", action_name(opts));
 	ret = write_ref_sha1(ref_lock, to, sb.buf);
+
 	strbuf_release(&sb);
 	return ret;
 }