diff --git a/nameko/testing/pytest.py b/nameko/testing/pytest.py
index <HASH>..<HASH> 100644
--- a/nameko/testing/pytest.py
+++ b/nameko/testing/pytest.py
@@ -322,7 +322,7 @@ def web_config(empty_config):
     port = find_free_port()
 
     cfg = empty_config
-    cfg[WEB_SERVER_CONFIG_KEY] = str(port)
+    cfg[WEB_SERVER_CONFIG_KEY] = "127.0.0.1:{}".format(port)
     return cfg
try explictly binding to <I>