diff --git a/mercurial/pvec.py b/mercurial/pvec.py
--- a/mercurial/pvec.py
+++ b/mercurial/pvec.py
@@ -182,7 +182,7 @@
 
 class pvec(object):
     def __init__(self, hashorctx):
-        if isinstance(hashorctx, str):
+        if isinstance(hashorctx, bytes):
             self._bs = hashorctx
             self._depth, self._vec = _split(util.b85decode(hashorctx))
         else: