diff --git a/CHANGELOG.md b/CHANGELOG.md
index b1c36df..56dc852 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,7 +2,10 @@
 
 ### Unreleased
 
-- 
+- The server now returns a ``50 PERMENANT FAILURE`` response when a client
+  requests a URL that does not exist on the server. This change is motivated by
+  mailing list discussions that a ``51 NOT FOUND`` status may not be
+  appropriate if the scheme/host component of the URL does not match the server.
 - Added ``-V`` / ``--version`` argument to display the version and exit.
 - Force URLs to always end in trailing slashes when serving a directory. This
   reduces duplicate selectors and makes resolving relative links more reliable.
diff --git a/jetforce.py b/jetforce.py
index bdaef13..d44b714 100755
--- a/jetforce.py
+++ b/jetforce.py
@@ -160,7 +160,7 @@ class JetforceApplication:
                         yield from response.body
                 break
         else:
-            send_status(Status.NOT_FOUND, "Not Found")
+            send_status(Status.PERMANENT_FAILURE, "URL not found on server")
 
     def route(
         self,