diff --git a/mercurial/hg.py b/mercurial/hg.py
--- a/mercurial/hg.py
+++ b/mercurial/hg.py
@@ -214,7 +214,7 @@
     else:
         dest = ui.expandpath(dest)
 
-    if isinstance(source, str):
+    if isinstance(source, bytes):
         origsource = ui.expandpath(source)
         source, branches = parseurl(origsource)
         srcrepo = repository(ui, source)