diff -r 15d3facfa40a -r aaad36b88298 mercurial/bundle2.py
--- a/mercurial/bundle2.py	Sun Jan 13 20:13:22 2019 -0500
+++ b/mercurial/bundle2.py	Wed Feb 20 19:28:51 2019 -0500
@@ -1397,8 +1397,8 @@
             assert chunknum == 0, 'Must start with chunk 0'
             self._chunkindex.append((0, self._tellfp()))
         else:
-            assert chunknum < len(self._chunkindex), \
-                   'Unknown chunk %d' % chunknum
+            assert chunknum < len(self._chunkindex), (
+                   'Unknown chunk %d' % chunknum)
             self._seekfp(self._chunkindex[chunknum][1])
 
         pos = self._chunkindex[chunknum][0]