diff --git a/prepare_repos.py b/prepare_repos.py
index 77ffac8d77fe94c7d2c686422f85795f7279ca50_cHJlcGFyZV9yZXBvcy5weQ==..f84110dd90bf8d0cf206deacca3c759b6f52d117_cHJlcGFyZV9yZXBvcy5weQ== 100644
--- a/prepare_repos.py
+++ b/prepare_repos.py
@@ -39,7 +39,8 @@
                 subprocess.check_call(['hg', 'clone', '--noupdate', clonedir,
                                        partialdir])
                 if revset != "same":
-                    subprocess.check_call(['hg', '--cwd', partialdir, 'strip',
+                    subprocess.check_call(['hg', '--cwd', partialdir,
+                                           '--config', 'extensions.strip=', 'strip',
                                            '--no-backup', '-r', revset])
                     subprocess.check_call(['hg', '--cwd', partialdir, 'debugupdatecache'])