diff -r dfb67cd1da7f -r 215f08c8006c mercurial/logcmdutil.py
--- a/mercurial/logcmdutil.py	Mon Jul 20 21:32:10 2020 -0700
+++ b/mercurial/logcmdutil.py	Mon Jul 20 21:33:28 2020 -0700
@@ -607,8 +607,6 @@
     if mapfile:
         return formatter.mapfile_templatespec(b'changeset', mapfile)
     else:
-        if pycompat.ispy3:
-            assert not isinstance(tmpl, str), b'tmpl must not be a str'
         return formatter.literal_templatespec(tmpl)