diff --git a/bonobo/commands/__init__.py b/bonobo/commands/__init__.py
index fb6de85..7017a5b 100644
--- a/bonobo/commands/__init__.py
+++ b/bonobo/commands/__init__.py
@@ -26,7 +26,9 @@ def entrypoint(args=None):
 
     commands = {}
 
-    def register_extension(ext, commands=commands):
+    def register_extension(ext):
+        nonlocal commands
+
         try:
             parser = subparsers.add_parser(ext.name)
             if isinstance(ext.plugin, type) and issubclass(ext.plugin, BaseCommand):