diff -r ab5bc57ba897 -r a019067fea9e hgext3rd/topic/topicmap.py
--- a/hgext3rd/topic/topicmap.py	Tue Mar 12 09:48:05 2019 -0700
+++ b/hgext3rd/topic/topicmap.py	Thu Mar 28 12:37:55 2019 +0100
@@ -9,6 +9,7 @@
     cmdutil,
     extensions,
     repoview,
+    util,
 )
 
 basefilter = set(['base', 'immutable'])
@@ -164,8 +165,13 @@
 
     def copy(self):
         """return an deep copy of the branchcache object"""
-        new = self.__class__(self, self.tipnode, self.tiprev, self.filteredhash,
-                             self._closednodes)
+        if util.safehasattr(self, '_entries'):
+            _entries = self._entries
+        else:
+            # hg <= 4.9 (624d6683c705, b137a6793c51)
+            _entries = self
+        new = self.__class__(_entries, self.tipnode, self.tiprev,
+                             self.filteredhash, self._closednodes)
         new.phaseshash = self.phaseshash
         return new