--- a/mercurial/filelog.py
+++ b/mercurial/filelog.py
@@ -65,6 +65,16 @@ class filelog(revlog):
             return (m["copy"], bin(m["copyrev"]))
         return False
 
+    def size(self, rev):
+        """return the size of a given revision"""
+
+        # for revisions with renames, we have to go the slow way
+        node = self.node(rev)
+        if self.renamed(node):
+            return len(self.read(node))
+
+        return revlog.size(self, rev)
+
     def cmp(self, node, text):
         """compare text with a given file revision"""