--- a/hgfastobs.py	Tue Feb 18 15:32:31 2014 -0800
+++ b/hgfastobs.py	Wed Feb 19 15:31:00 2014 -0500
@@ -61,9 +61,9 @@
     return cs
 
 def _revsetprecursors(repo, subset, x):
-    s = revset.getset(repo, range(len(repo)), x)
+    s = revset.getset(repo, revset.baseset(range(len(repo))), x)
     cs = _precursors(repo, s)
-    return [r for r in subset if r in cs]
+    return revset.baseset([r for r in subset if r in cs])
 
 revset.symbols['_fastobs_precursors'] = _revsetprecursors