--- a/hgext3rd/topic/flow.py	Fri Jul 12 23:24:04 2019 -0700
+++ b/hgext3rd/topic/flow.py	Sat Jul 13 00:17:03 2019 -0700
@@ -11,8 +11,13 @@
 
 from mercurial.i18n import _
 
+from . import (
+    compat,
+)
+
 def enforcesinglehead(repo, tr):
-    for name, heads in repo.filtered('visible').branchmap().iteritems():
+    branchmap = repo.filtered('visible').branchmap()
+    for name, heads in compat.branchmapitems(branchmap):
         if len(heads) > 1:
             hexs = [node.short(n) for n in heads]
             raise error.Abort(_('%d heads on "%s"') % (len(heads), name),