diff -r adbcba130143 Lib/difflib.py
--- a/Lib/difflib.py	Tue Mar 29 12:09:45 2011 -0700
+++ b/Lib/difflib.py	Sat Apr 02 13:53:46 2011 +0200
@@ -913,7 +913,10 @@
         cruncher = SequenceMatcher(self.linejunk, a, b)
         for tag, alo, ahi, blo, bhi in cruncher.get_opcodes():
             if tag == 'replace':
-                g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
+                if ahi - alo + bhi - blo < 100:
+                    g = self._fancy_replace(a, alo, ahi, b, blo, bhi)
+                else:
+                    g = self._plain_replace(a, alo, ahi, b, blo, bhi)
             elif tag == 'delete':
                 g = self._dump('-', a, alo, ahi)
             elif tag == 'insert':