diff -r a263f4c0f2ee -r fd602980f7ee hgext3rd/topic/__init__.py
--- a/hgext3rd/topic/__init__.py	Sun Jun 18 03:20:52 2017 +0530
+++ b/hgext3rd/topic/__init__.py	Sun Jun 18 03:23:46 2017 +0530
@@ -282,6 +282,10 @@
         l = repo.lock()
         txn = repo.transaction('rewrite-topics')
         try:
+            newp = None
+            oldp = None
+            p1 = None
+            p2 = None
             for c in repo.set('%r', change):
                 def filectxfn(repo, ctx, path):
                     try:
@@ -309,11 +313,25 @@
                 ui.debug('changing topic of %s from %s to %s\n' % (
                     c, oldtopic, newtopic))
                 ui.debug('fixedextra: %r\n' % fixedextra)
+                # While changing topic of set of linear commits, make sure that
+                # we base our commits on new parent rather than old parent which
+                # was obsoleted while changing the topic
+                if newp and c.p1().node() == oldp:
+                    p1 = newp
+                    p2 = c.p2().node()
+                elif newp and c.p2().node() == oldp:
+                    p1 = c.p1().node()
+                    p2 = newp
+                else:
+                    p1 = c.p1().node()
+                    p2 = c.p2().node()
                 mc = context.memctx(
-                    repo, (c.p1().node(), c.p2().node()), c.description(),
+                    repo, (p1, p2), c.description(),
                     c.files(), filectxfn,
                     user=c.user(), date=c.date(), extra=fixedextra)
                 newnode = repo.commitctx(mc)
+                oldp = c.node()
+                newp = newnode
                 ui.debug('new node id is %s\n' % node.hex(newnode))
                 needevolve = needevolve or (len(c.children()) > 0)
                 obsolete.createmarkers(repo, [(c, (repo[newnode],))])