--- a/mercurial/revlog.py+++ b/mercurial/revlog.py@@ -784,6 +784,10 @@ class revlog: continue delta = chunk[80:]+ for p in (p1, p2):+ if not p in self.nodemap:+ raise RevlogError(_("unknown parent %s") % short(p1))+ if not chain: # retrieve the parent revision of the delta chain chain = p1