diff --git a/mercurial/wireproto.py b/mercurial/wireproto.py
--- a/mercurial/wireproto.py
+++ b/mercurial/wireproto.py
@@ -587,7 +587,7 @@
 
     return ui.configbool('server', 'bundle1')
 
-def supportedcompengines(ui, proto, role):
+def supportedcompengines(ui, role):
     """Obtain the list of supported compression engines for a request."""
     assert role in (util.CLIENTROLE, util.SERVERROLE)
 
@@ -824,7 +824,7 @@
         # FUTURE advertise minrx and mintx after consulting config option
         caps.append('httpmediatype=0.1rx,0.1tx,0.2tx')
 
-        compengines = supportedcompengines(repo.ui, proto, util.SERVERROLE)
+        compengines = supportedcompengines(repo.ui, util.SERVERROLE)
         if compengines:
             comptypes = ','.join(urlreq.quote(e.wireprotosupport().name)
                                  for e in compengines)
diff --git a/mercurial/wireprotoserver.py b/mercurial/wireprotoserver.py
--- a/mercurial/wireprotoserver.py
+++ b/mercurial/wireprotoserver.py
@@ -192,7 +192,7 @@
                     break
 
             # Now find an agreed upon compression format.
-            for engine in wireproto.supportedcompengines(self._ui, self,
+            for engine in wireproto.supportedcompengines(self._ui,
                                                          util.SERVERROLE):
                 if engine.wireprotosupport().name in compformats:
                     opts = {}