diff --git a/lockfile.c b/lockfile.c
index 9268cdf325..aa69210d8b 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -174,8 +174,16 @@ int hold_lock_file_for_update_timeout(struct lock_file *lk, const char *path,
 				      int flags, long timeout_ms)
 {
 	int fd = lock_file_timeout(lk, path, flags, timeout_ms);
-	if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
-		unable_to_lock_die(path, errno);
+	if (fd < 0) {
+		if (flags & LOCK_DIE_ON_ERROR)
+			unable_to_lock_die(path, errno);
+		if (flags & LOCK_REPORT_ON_ERROR) {
+			struct strbuf buf = STRBUF_INIT;
+			unable_to_lock_message(path, errno, &buf);
+			error("%s", buf.buf);
+			strbuf_release(&buf);
+		}
+	}
 	return fd;
 }
 
diff --git a/lockfile.h b/lockfile.h
index d26ad27b2b..16775a7d79 100644
--- a/lockfile.h
+++ b/lockfile.h
@@ -129,10 +129,16 @@ struct lock_file {
 /*
  * If a lock is already taken for the file, `die()` with an error
  * message. If this flag is not specified, trying to lock a file that
- * is already locked returns -1 to the caller.
+ * is already locked silently returns -1 to the caller, or ...
  */
 #define LOCK_DIE_ON_ERROR 1
 
+/*
+ * ... this flag can be passed instead to return -1 and give the usual
+ * error message upon an error.
+ */
+#define LOCK_REPORT_ON_ERROR 2
+
 /*
  * Usually symbolic links in the destination path are resolved. This
  * means that (1) the lockfile is created by adding ".lock" to the
diff --git a/merge.c b/merge.c
index 23866c9165..04ee5fc911 100644
--- a/merge.c
+++ b/merge.c
@@ -57,7 +57,7 @@ int checkout_fast_forward(const unsigned char *head,
 
 	refresh_cache(REFRESH_QUIET);
 
-	if (hold_locked_index(lock_file, 0) < 0)
+	if (hold_locked_index(lock_file, LOCK_REPORT_ON_ERROR) < 0)
 		return -1;
 
 	memset(&trees, 0, sizeof(trees));