mercurial/revlog.py

--- a/mercurial/revlog.py	Tue May 17 11:06:59 2005 -0800
+++ b/mercurial/revlog.py	Tue May 17 11:40:26 2005 -0800
@@ -411,6 +411,8 @@
 
         # retrieve the parent revision of the delta chain
         chain = data[24:44]
+        if not chain in self.nodemap:
+            raise "unknown base %s" % short(chain[:4])
 
         # track the base of the current delta log
         r = self.count()