diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -4558,6 +4558,7 @@ table = {
         (debugwireargs,
          [('', 'three', '', 'three'),
           ('', 'four', '', 'four'),
+          ('', 'five', '', 'five'),
           ] + remoteopts,
          _('REPO [OPTIONS]... [ONE [TWO]]')),
     "^diff":
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1921,9 +1921,9 @@ class localrepository(repo.repository):
     def listkeys(self, namespace):
         return pushkey.list(self, namespace)
 
-    def debugwireargs(self, one, two, three=None, four=None):
+    def debugwireargs(self, one, two, three=None, four=None, five=None):
         '''used to test argument passing over the wire'''
-        return "%s %s %s %s" % (one, two, three, four)
+        return "%s %s %s %s %s" % (one, two, three, four, five)
 
 # used to avoid circular references so destructors work
 def aftertrans(files):
diff --git a/mercurial/wireproto.py b/mercurial/wireproto.py
--- a/mercurial/wireproto.py
+++ b/mercurial/wireproto.py
@@ -159,7 +159,7 @@ class wirerepository(repo.repository):
             self.ui.status(_('remote: '), l)
         return ret
 
-    def debugwireargs(self, one, two, three=None, four=None):
+    def debugwireargs(self, one, two, three=None, four=None, five=None):
         # don't pass optional arguments left at their default value
         opts = {}
         if three is not None:
diff --git a/tests/test-wireproto.t b/tests/test-wireproto.t
--- a/tests/test-wireproto.t
+++ b/tests/test-wireproto.t
@@ -8,11 +8,13 @@ Setup repo:
 Local:
 
   $ hg debugwireargs repo eins zwei --three drei --four vier
-  eins zwei drei vier
+  eins zwei drei vier None
   $ hg debugwireargs repo eins zwei --four vier
-  eins zwei None vier
+  eins zwei None vier None
   $ hg debugwireargs repo eins zwei
-  eins zwei None None
+  eins zwei None None None
+  $ hg debugwireargs repo eins zwei --five fuenf
+  eins zwei None None fuenf
 
 HTTP:
 
@@ -20,11 +22,13 @@ HTTP:
   $ cat hg1.pid >> $DAEMON_PIDS
 
   $ hg debugwireargs http://localhost:$HGPORT/ un deux trois quatre
-  un deux trois quatre
+  un deux trois quatre None
   $ hg debugwireargs http://localhost:$HGPORT/ eins zwei --four vier
-  eins zwei None vier
+  eins zwei None vier None
   $ hg debugwireargs http://localhost:$HGPORT/ eins zwei
-  eins zwei None None
+  eins zwei None None None
+  $ hg debugwireargs http://localhost:$HGPORT/ eins zwei --five fuenf
+  eins zwei None None None
   $ cat access.log
   * - - [*] "GET /?cmd=capabilities HTTP/1.1" 200 - (glob)
   * - - [*] "GET /?cmd=debugwireargs&four=quatre&one=un&three=trois&two=deux HTTP/1.1" 200 - (glob)
@@ -35,6 +39,9 @@ HTTP:
   * - - [*] "GET /?cmd=capabilities HTTP/1.1" 200 - (glob)
   * - - [*] "GET /?cmd=debugwireargs&one=eins&two=zwei HTTP/1.1" 200 - (glob)
   * - - [*] "GET /?cmd=debugwireargs&one=eins&two=zwei HTTP/1.1" 200 - (glob)
+  * - - [*] "GET /?cmd=capabilities HTTP/1.1" 200 - (glob)
+  * - - [*] "GET /?cmd=debugwireargs&one=eins&two=zwei HTTP/1.1" 200 - (glob)
+  * - - [*] "GET /?cmd=debugwireargs&one=eins&two=zwei HTTP/1.1" 200 - (glob)
 
 SSH (try to exercise the ssh functionality with a dummy script):
 
@@ -52,9 +59,11 @@ SSH (try to exercise the ssh functionali
   > EOF
 
   $ hg debugwireargs --ssh "python ./dummyssh" ssh://user@dummy/repo uno due tre quattro
-  uno due tre quattro
+  uno due tre quattro None
   $ hg debugwireargs --ssh "python ./dummyssh" ssh://user@dummy/repo eins zwei --four vier
-  eins zwei None vier
+  eins zwei None vier None
   $ hg debugwireargs --ssh "python ./dummyssh" ssh://user@dummy/repo eins zwei
-  eins zwei None None
+  eins zwei None None None
+  $ hg debugwireargs --ssh "python ./dummyssh" ssh://user@dummy/repo eins zwei --five fuenf
+  eins zwei None None None