--- a/mercurial/revlog.py	Thu Jan 04 16:29:03 2018 -0800
+++ b/mercurial/revlog.py	Mon Dec 25 16:31:14 2017 -0700
@@ -622,12 +622,14 @@
 
     def parentrevs(self, rev):
         try:
-            return self.index[rev][5:7]
+            entry = self.index[rev]
         except IndexError:
             if rev == wdirrev:
                 raise error.WdirUnsupported
             raise
 
+        return entry[5], entry[6]
+
     def node(self, rev):
         try:
             return self.index[rev][7]