diff --git a/synapse/rest/client/v1/logout.py b/synapse/rest/client/v1/logout.py
index ca49955935a332a4f11cd8a3d72cf5b12e31ce88..e092158cb786180439c68d899a74c3da56906dc2 100644
--- a/synapse/rest/client/v1/logout.py
+++ b/synapse/rest/client/v1/logout.py
@@ -44,7 +44,10 @@ class LogoutRestServlet(ClientV1RestServlet):
             requester = yield self.auth.get_user_by_req(request)
         except AuthError:
             # this implies the access token has already been deleted.
-            pass
+            defer.returnValue((401, {
+                "errcode": "M_UNKNOWN_TOKEN",
+                "error": "Access Token unknown or expired"
+            }))
         else:
             if requester.device_id is None:
                 # the acccess token wasn't associated with a device.