--- a/mercurial/revlog.py	Sun Feb 10 22:41:51 2019 -0800
+++ b/mercurial/revlog.py	Tue Feb 12 11:27:27 2019 -0800
@@ -1340,7 +1340,7 @@
             return True
 
         def maybewdir(prefix):
-            return all(c == 'f' for c in prefix)
+            return all(c == 'f' for c in pycompat.iterbytestr(prefix))
 
         hexnode = hex(node)