diff -r 4864ddc4c6d9 -r 2a07df823588 hgext3rd/topic/destination.py
--- a/hgext3rd/topic/destination.py	Mon Aug 15 05:25:53 2016 +0200
+++ b/hgext3rd/topic/destination.py	Mon Aug 15 00:19:44 2016 +0200
@@ -13,7 +13,12 @@
 def _destmergebranch(orig, repo, action='merge', sourceset=None,
                      onheadcheck=True, destspace=None):
     # XXX: take destspace into account
-    p1 = repo['.']
+    if sourceset is None:
+       p1 = repo['.']
+    else:
+        # XXX: using only the max here is flacky. That code should eventually
+        # be updated to take care of the whole sourceset.
+       p1 =  repo[max(sourceset)]
     top = p1.topic()
     if top:
         revs = repo.revs('topic(%s) - obsolete()', top)