diff --git a/mercurial/extensions.py b/mercurial/extensions.py
--- a/mercurial/extensions.py
+++ b/mercurial/extensions.py
@@ -221,14 +221,7 @@ def _runextsetup(name, ui):
     extsetup = getattr(_extensions[name], 'extsetup', None)
     if extsetup:
         try:
-            try:
-                extsetup(ui)
-            except TypeError:
-                if pycompat.getargspec(extsetup).args:
-                    raise
-                ui.deprecwarn("extsetup for '%s' must take a ui argument"
-                              % name, "4.9")
-                extsetup() # old extsetup with no ui argument
+            extsetup(ui)
         except Exception as inst:
             ui.traceback(force=True)
             msg = stringutil.forcebytestr(inst)