diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -691,6 +691,9 @@
     def flags(self, rev):
         return self.index[rev][0] & 0xFFFF
 
+    # fast flag(rev) where rev isn't filtered
+    _uncheckedflags = flags
+
     def length(self, rev):
         return self.index[rev][1]