diff --git a/mercurial/filelog.py b/mercurial/filelog.py
--- a/mercurial/filelog.py
+++ b/mercurial/filelog.py
@@ -5,8 +5,8 @@
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
-import error, revlog
-import re
+import error, mdiff, revlog
+import re, struct
 
 _mdre = re.compile('\1\n')
 def parsemeta(text):
@@ -107,3 +107,23 @@ class filelog(revlog.revlog):
     def iscensored(self, rev):
         """Check if a file revision is censored."""
         return self.flags(rev) & revlog.REVIDX_ISCENSORED
+
+    def _peek_iscensored(self, baserev, delta, flush):
+        """Quickly check if a delta produces a censored revision."""
+        # Fragile heuristic: unless new file meta keys are added alphabetically
+        # preceding "censored", all censored revisions are prefixed by
+        # "\1\ncensored:". A delta producing such a censored revision must be a
+        # full-replacement delta, so we inspect the first and only patch in the
+        # delta for this prefix.
+        hlen = struct.calcsize(">lll")
+        if len(delta) <= hlen:
+            return False
+
+        oldlen = self.rawsize(baserev)
+        newlen = len(delta) - hlen
+        if delta[:hlen] != mdiff.replacediffheader(oldlen, newlen):
+            return False
+
+        add = "\1\ncensored:"
+        addlen = len(add)
+        return newlen >= addlen and delta[hlen:hlen + addlen] == add
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -1386,7 +1386,10 @@ class revlog(object):
             transaction.add(self.indexfile, isize, r)
             transaction.add(self.datafile, end)
             dfh = self.opener(self.datafile, "a")
-
+        def flush():
+            if dfh:
+                dfh.flush()
+            ifh.flush()
         try:
             # loop through our set of deltas
             chain = None
@@ -1430,9 +1433,13 @@ class revlog(object):
                         raise error.CensoredBaseError(self.indexfile,
                                                       self.node(baserev))
 
+                flags = REVIDX_DEFAULT_FLAGS
+                if self._peek_iscensored(baserev, delta, flush):
+                    flags |= REVIDX_ISCENSORED
+
                 chain = self._addrevision(node, None, transaction, link,
-                                          p1, p2, REVIDX_DEFAULT_FLAGS,
-                                          (baserev, delta), ifh, dfh)
+                                          p1, p2, flags, (baserev, delta),
+                                          ifh, dfh)
                 if not dfh and not self._inline:
                     # addrevision switched from inline to conventional
                     # reopen the index
@@ -1450,6 +1457,10 @@ class revlog(object):
         """Check if a file revision is censored."""
         return False
 
+    def _peek_iscensored(self, baserev, delta, flush):
+        """Quickly check if a delta produces a censored revision."""
+        return False
+
     def getstrippoint(self, minlink):
         """find the minimum rev that must be stripped to strip the linkrev