diff --git a/mercurial/filelog.py b/mercurial/filelog.py
--- a/mercurial/filelog.py
+++ b/mercurial/filelog.py
@@ -64,7 +64,7 @@ class filelog(revlog.revlog):
         node = self.node(rev)
         if self.renamed(node):
             return len(self.read(node))
-        if self._iscensored(rev):
+        if self.iscensored(rev):
             return 0
 
         # XXX if self.read(node).startswith("\1\n"), this returns (size+4)
@@ -85,7 +85,7 @@ class filelog(revlog.revlog):
             return False
 
         # censored files compare against the empty file
-        if self._iscensored(self.rev(node)):
+        if self.iscensored(self.rev(node)):
             return text != ''
 
         # renaming a file produces a different hash, even if the data
@@ -104,6 +104,6 @@ class filelog(revlog.revlog):
                 raise error.CensoredNodeError(self.indexfile, node)
             raise
 
-    def _iscensored(self, rev):
+    def iscensored(self, rev):
         """Check if a file revision is censored."""
         return self.flags(rev) & revlog.REVIDX_ISCENSORED
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -1419,6 +1419,10 @@ class revlog(object):
 
         return content
 
+    def iscensored(self, rev):
+        """Check if a file revision is censored."""
+        return False
+
     def getstrippoint(self, minlink):
         """find the minimum rev that must be stripped to strip the linkrev
 
diff --git a/mercurial/unionrepo.py b/mercurial/unionrepo.py
--- a/mercurial/unionrepo.py
+++ b/mercurial/unionrepo.py
@@ -160,6 +160,12 @@ class unionfilelog(unionrevlog, filelog.
     def baserevdiff(self, rev1, rev2):
         return filelog.filelog.revdiff(self, rev1, rev2)
 
+    def iscensored(self, rev):
+        """Check if a revision is censored."""
+        if rev <= self.repotiprev:
+            return filelog.filelog.iscensored(self, rev)
+        return self.revlog2.iscensored(rev)
+
 class unionpeer(localrepo.localpeer):
     def canpush(self):
         return False