diff --git a/src/filelock.c b/src/filelock.c
index dcf3c658ce0..becdbc73bd6 100644
--- a/src/filelock.c
+++ b/src/filelock.c
@@ -514,6 +514,8 @@ lock_if_free (clasher, lfname)
         }
       else if (locker == 1)
         return 1;  /* Someone else has it.  */
+      else if (locker == -1)
+      return -1;   /* current_lock_owner() returned strange error */
 
       /* We deleted a stale lock; try again to lock the file.  */
     }