diff --git a/radicale/__init__.py b/radicale/__init__.py
index f15f6480..706759a1 100644
--- a/radicale/__init__.py
+++ b/radicale/__init__.py
@@ -242,7 +242,7 @@ class Application(object):
             headers["Content-Length"] = str(len(answer))
 
         # Start response
-        status = "%i %s" % (status, client.responses.get(status, ""))
+        status = "%i %s" % (status, client.responses.get(status, "Unknown"))
         start_response(status, list(headers.items()))
 
         # Return response content