--- a/mercurial/tags.py	Tue Feb 12 19:08:17 2019 +0100
+++ b/mercurial/tags.py	Tue Mar 05 03:33:41 2019 +0530
@@ -548,7 +548,7 @@
 
 def _tag(repo, names, node, message, local, user, date, extra=None,
          editor=False):
-    if isinstance(names, str):
+    if isinstance(names, bytes):
         names = (names,)
 
     branches = repo.branchmap()