--- a/mercurial/destutil.py	Fri Jan 19 17:09:24 2018 +0100
+++ b/mercurial/destutil.py	Fri Jan 19 17:29:50 2018 +0100
@@ -359,7 +359,7 @@
 
 def stackbase(ui, repo):
     revs = stack.getstack(repo)
-    return revs.last() if revs else None
+    return revs.first() if revs else None
 
 def _statusotherbook(ui, repo):
     bmheads = bookmarks.headsforactive(repo)

--- a/mercurial/stack.py	Fri Jan 19 17:09:24 2018 +0100
+++ b/mercurial/stack.py	Fri Jan 19 17:29:50 2018 +0100
@@ -13,8 +13,8 @@
 )
 
 def getstack(repo, rev=None):
-    """return a smartrev of the stack containing either rev if it is not None
-    or the current working directory parent.
+    """return a sorted smartrev of the stack containing either rev if it is
+    not None or the current working directory parent.
 
     The stack will always contain all drafts changesets which are ancestors to
     the revision and are not merges.
@@ -24,4 +24,6 @@
 
     revspec = 'reverse(only(%s) and not public() and not ::merge())'
     revset = revsetlang.formatspec(revspec, rev)
-    return scmutil.revrange(repo, [revset])
+    revisions = scmutil.revrange(repo, [revset])
+    revisions.sort()
+    return revisions

--- a/tests/test-stack.t	Fri Jan 19 17:09:24 2018 +0100
+++ b/tests/test-stack.t	Fri Jan 19 17:29:50 2018 +0100
@@ -205,13 +205,13 @@
   ~
 Check the stack order
   $ hg log -r "first(stack())"
-  10 foo draft c_h
+  9 foo draft c_g
   $ hg log -r "first(stack(10))"
-  10 foo draft c_h
+  9 foo draft c_g
   $ hg log -r "first(stack(8))"
-  8 foo draft c_f
+  7 foo draft c_e
   $ hg log -r "first(stack(head()))"
-  8 foo draft c_f
+  7 foo draft c_e
 
 Case with multiple heads with unstability involved
 --------------------------------------------------