diff --git a/subcmds/sync.py b/subcmds/sync.py
index ecb89a1..ad05cad 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -217,6 +217,10 @@
             missing.append(project)
         self._Fetch(missing)
 
+    if self.manifest.IsMirror:
+      # bail out now, we have no working tree
+      return
+
     if self.UpdateProjectList():
       sys.exit(1)