diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -31,7 +31,7 @@ def _revancestors(repo, revs, followfirs
             revsnode = revqueue.popleft()
             heapq.heappush(h, -revsnode)
 
-        seen = set([node.nullrev])
+        seen = set()
         while h:
             current = -heapq.heappop(h)
             if current not in seen:
diff --git a/tests/test-log.t b/tests/test-log.t
--- a/tests/test-log.t
+++ b/tests/test-log.t
@@ -635,6 +635,20 @@ log -f -r 1:tip
   
 
 
+log -f -r null
+
+  $ hg log -f -r null
+  changeset:   -1:000000000000
+  user:        
+  date:        Thu Jan 01 00:00:00 1970 +0000
+  
+  $ hg log -f -r null -G
+  o  changeset:   -1:000000000000
+     user:
+     date:        Thu Jan 01 00:00:00 1970 +0000
+  
+
+
 log -r .  with two parents
 
   $ hg up -C 3
diff --git a/tests/test-revset.t b/tests/test-revset.t
--- a/tests/test-revset.t
+++ b/tests/test-revset.t
@@ -477,6 +477,10 @@ Test explicit numeric revision
   hg: parse error: rev expects a number
   [255]
 
+Test null revision
+  $ log 'ancestors(null)'
+  -1
+
   $ log 'outgoing()'
   8
   9