diff --git a/mercurial/linelog.py b/mercurial/linelog.py
--- a/mercurial/linelog.py
+++ b/mercurial/linelog.py
@@ -296,6 +296,7 @@
         else:
             ar = self.annotate(rev)
             #        ar = self.annotate(self._maxrev)
+        programlen = self._program.__len__
         if a1 > len(ar.lines):
             raise LineLogError(
                 '%d contains %d lines, tried to access line %d' % (
@@ -308,7 +309,7 @@
         else:
             a1info = ar.lines[a1]
             a1inst = self._program[a1info._offset]
-        oldproglen = len(self._program)
+        oldproglen = programlen()
         appendinst = self._program.append
 
         # insert