diff --git a/hgext/git/manifest.py b/hgext/git/manifest.py
--- a/hgext/git/manifest.py
+++ b/hgext/git/manifest.py
@@ -1,6 +1,7 @@
 from __future__ import absolute_import
 
 from mercurial import (
+    error,
     match as matchmod,
     pathutil,
     pycompat,
@@ -217,7 +218,7 @@
             return b''
 
     def copy(self):
-        pass
+        return gittreemanifest(self._git_repo, self._tree, dict(self._pending_changes))
 
     def items(self):
         for f in self: