diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -2024,8 +2024,8 @@
     def __init__(self, repo, wrappedctx):
         super(overlayworkingctx, self).__init__(repo)
         self._repo = repo
+        self.clean()
         self._wrappedctx = wrappedctx
-        self._clean()
 
     def data(self, path):
         if self.isdirty(path):
@@ -2105,7 +2105,7 @@
     def isdirty(self, path):
         return path in self._cache
 
-    def _clean(self):
+    def clean(self):
         self._cache = {}
 
     def _markdirty(self, path, exists, data=None, date=None, flags=''):