diff --git a/django/test/client.py b/django/test/client.py
index 7d50ccb326..d56472c1ae 100644
--- a/django/test/client.py
+++ b/django/test/client.py
@@ -193,7 +193,7 @@ class Client(object):
         using the arguments to the request.
         """
         environ = {
-            'HTTP_COOKIE':      self.cookies,
+            'HTTP_COOKIE':       self.cookies.output(header='', sep='; '),
             'PATH_INFO':         '/',
             'QUERY_STRING':      '',
             'REMOTE_ADDR':       '127.0.0.1',