diff --git a/Lib/lib2to3/refactor.py b/Lib/lib2to3/refactor.py
index da05bc35e28..97c9e122bd6 100755
--- a/Lib/lib2to3/refactor.py
+++ b/Lib/lib2to3/refactor.py
@@ -172,7 +172,9 @@ class RefactoringTool(object):
           want a pre-order AST traversal, and post_order is the list that want
           post-order traversal.
         """
-        fixer_pkg = ".".join(self.fixer_dir.split(os.path.sep))
+        fixer_pkg = self.fixer_dir.replace(os.path.sep, ".")
+        if os.path.altsep:
+            fixer_pkg = self.fixer_dir.replace(os.path.altsep, ".")
         pre_order_fixers = []
         post_order_fixers = []
         fix_names = self.options.fix