diff --git a/git_cache.py b/git_cache.py
index c33252035..89f7f6d79 100755
--- a/git_cache.py
+++ b/git_cache.py
@@ -308,6 +308,8 @@ class Mirror(object):
                            tempdir)
       if code:
         return False
+      # A quick validation that all references are valid.
+      self.RunGit(['for-each-ref'], cwd=tempdir)
     except Exception as e:
       self.print('Encountered error: %s' % str(e), file=sys.stderr)
       gclient_utils.rmtree(tempdir)