--- a/hgext3rd/topic/revset.py	Sun Dec 16 11:22:04 2018 +0800
+++ b/hgext3rd/topic/revset.py	Wed Dec 26 22:14:23 2018 +0800
@@ -116,8 +116,6 @@
         (e.g. when stack index is too high), this returns empty set to be more
         revset-friendly.
         """
-        if n < 0:
-            return revset.baseset()
         s = revset.getset(repo, revset.fullreposet(repo), x)
         if not s:
             return revset.baseset()
@@ -128,8 +126,12 @@
                 st = stack.stack(repo, topic=topic)
             else:
                 st = stack.stack(repo, branch=repo[r].branch())
+            if n < 0:
+                st = list(st)[1:]
+            else:
+                st = list(st)
             try:
-                rev = list(st)[n]
+                rev = st[n]
             except IndexError:
                 continue
             if rev == -1 and n == 0:

--- a/tests/test-topic.t	Sun Dec 16 11:22:04 2018 +0800
+++ b/tests/test-topic.t	Wed Dec 26 22:14:23 2018 +0800
@@ -865,6 +865,10 @@
   0: 
   $ tlog 'tip#stack[2]'
   4: 
+  $ tlog 'tip#stack[-1]'
+  4: 
+  $ tlog 'tip#stack[-2]'
+  0: 
 
   $ hg stack featureA
   ### topic: featureA
@@ -876,20 +880,24 @@
 
   $ tlog 'featureA#s[0]'
   0: 
-  $ tlog 'featureA#s[1]'
+  $ tlog 'featureA#s[1] and featureA#s[-3]'
   1: featureA
-  $ tlog 'featureA#s[2]'
+  $ tlog 'featureA#s[2] and featureA#s[-2]'
   2: featureA
-  $ tlog 'featureA#s[3]'
+  $ tlog 'featureA#s[3] and featureA#s[-1]'
   3: featureA
+  $ tlog 'featureA#s[-4]'
 
   $ tlog 'all()#s[-1]'
+  3: featureA
+  4: 
   $ tlog 'all()#s[0]'
   0: 
   $ tlog 'all()#s[1]'
   0: 
   1: featureA
   $ tlog 'all()#s[9999]'
+  $ tlog 'all()#s[-9999]'
 
   $ hg topic featureB
   marked working directory as topic: featureB