diff --git a/tests/http_mock.py b/tests/http_mock.py
index b059b5fa8..9b8250ee1 100644
--- a/tests/http_mock.py
+++ b/tests/http_mock.py
@@ -55,7 +55,14 @@ def request(self, uri,
     self.uri = uri
     self.method = method
     self.body = body
+
+    # NB: reproduce the header normalization behavior
+    if headers is None:
+      headers = {}
+    else:
+      headers = httplib2._normalize_headers(headers)
     self.headers = headers
+
     return httplib2.Response(self.response_headers), self.data