diff --git a/testing/fixtures.py b/testing/fixtures.py
index ef5a0418..5182a083 100644
--- a/testing/fixtures.py
+++ b/testing/fixtures.py
@@ -38,7 +38,7 @@ def copy_tree_to_path(src_dir, dest_dir):
 
 def git_dir(tempdir_factory):
     path = tempdir_factory.get()
-    cmd_output('git', 'init', path)
+    cmd_output('git', '-c', 'init.defaultBranch=master', 'init', path)
     return path