diff --git a/hgext3rd/fbamend/__init__.py b/hgext3rd/fbamend/__init__.py
--- a/hgext3rd/fbamend/__init__.py
+++ b/hgext3rd/fbamend/__init__.py
@@ -184,6 +184,7 @@
 def amend(ui, repo, *pats, **opts):
     '''amend the current changeset with more changes
     '''
+    # 'rebase' is a tristate option: None=auto, True=force, False=disable
     rebase = opts.get('rebase')
     to = opts.get('to')
 
@@ -263,6 +264,21 @@
             ui.status(_("nothing changed\n"))
             return 1
 
+        if haschildren and rebase is None and not _histediting(repo):
+            # If the user has chosen the default behaviour for the
+            # rebase, then see if we can apply any heuristics. This
+            # will not performed if a histedit is in flight.
+
+            newcommit = repo[node]
+            # If the rebase did not change the manifest and the
+            # working copy is clean, force the children to be
+            # restacked.
+            if (old.manifestnode() == newcommit.manifestnode() and
+                not repo[None].dirty()):
+                ui.status(_('amend did not change the manifest, children '
+                            'commits will be restacked automatically\n'))
+                rebase = True
+
         if haschildren and not rebase:
             msg = _("warning: the changeset's children were left behind\n")
             if _histediting(repo):
diff --git a/tests/test-fbamend-nextrebase.t b/tests/test-fbamend-nextrebase.t
--- a/tests/test-fbamend-nextrebase.t
+++ b/tests/test-fbamend-nextrebase.t
@@ -35,7 +35,7 @@
   $ hg debugbuilddag -n +4
   $ hg up 1
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg next
@@ -89,7 +89,7 @@
   $ hg debugbuilddag -n +5
   $ hg up 1
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg next --rebase --top
@@ -115,7 +115,7 @@
   $ hg debugbuilddag -n +5
   $ hg up 1
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg next --rebase
@@ -165,7 +165,7 @@
   $ hg debugbuilddag -n +6
   $ hg up 1
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg next --rebase 2
@@ -216,7 +216,7 @@
   $ hg debugbuilddag -n +5
   $ hg up 1
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amend 1"
+  $ hg amend -m "amend 1" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg amend -m "amend 2"
@@ -257,7 +257,7 @@
   $ hg debugbuilddag -n +6
   $ hg up 2
   3 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg up 0
@@ -303,7 +303,7 @@
   $ hg debugbuilddag -n +6
   $ hg up 1
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ mkcommit a
@@ -365,7 +365,7 @@
   0 files updated, 0 files merged, 2 files removed, 0 files unresolved
   $ echo "conflict" > c
   $ hg add c
-  $ hg amend -m "amended to add c"
+  $ hg amend -m "amended to add c" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ showgraph
diff --git a/tests/test-fbamend-noinhibit.t b/tests/test-fbamend-noinhibit.t
--- a/tests/test-fbamend-noinhibit.t
+++ b/tests/test-fbamend-noinhibit.t
@@ -12,7 +12,7 @@
   $ hg debugbuilddag -m +3
   $ hg update 1
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "Amended"
+  $ hg amend -m "Amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg rebase --restack
diff --git a/tests/test-fbamend-restack.t b/tests/test-fbamend-restack.t
--- a/tests/test-fbamend-restack.t
+++ b/tests/test-fbamend-restack.t
@@ -448,12 +448,12 @@
   $ hg prev
   0 files updated, 0 files merged, 1 files removed, 0 files unresolved
   [*] add b (glob)
-  $ hg amend -m "successor 1"
+  $ hg amend -m "successor 1" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg up 1
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "successor 2"
+  $ hg amend -m "successor 2" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg up 1
@@ -687,10 +687,10 @@
   > A
   > EOS
   $ hg update B -q
-  $ hg commit --amend -m B2 -q 2>/dev/null
+  $ hg commit --amend -m B2 -q --no-rebase 2>/dev/null
   $ hg tag --local B2
   $ hg rebase -r C -d B2 -q
-  $ hg commit --amend -m B3 -q 2>/dev/null
+  $ hg commit --amend -m B3 -q --no-rebase 2>/dev/null
   $ hg tag --local B3
   $ showgraph
   @  6 B3
@@ -867,3 +867,54 @@
   | o  2 C
   |/
   o  0 A
+
+Test auto-restack heuristics - no changes to manifest and clean working directory
+  $ reset
+  $ mkcommit a
+  $ mkcommit b
+  $ mkcommit c
+  $ hg prev
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  [7c3bad] add b
+  $ hg amend -m 'Unchanged manifest for b'
+  amend did not change the manifest, children commits will be restacked automatically
+  rebasing 2:4538525df7e2 "add c"
+  $ hg prev
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  [1f0dee] add a
+  $ hg amend -m 'Unchanged manifest for a'
+  amend did not change the manifest, children commits will be restacked automatically
+  rebasing 3:0024b613eb65 "Unchanged manifest for b"
+  rebasing 4:3fcb618bdf2b "add c"
+
+Test auto-restack heuristics - manifest changes
+  $ reset
+  $ mkcommit a
+  $ mkcommit b
+  $ mkcommit c
+  $ hg prev
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  [7c3bad] add b
+  $ echo 'new b' > b
+  $ hg amend -m 'Change manifest for b'
+  warning: the changeset's children were left behind
+  (use 'hg restack' to rebase them)
+
+Test auto-restack heuristics - no committed changes to manifest but dirty working directory
+  $ reset
+  $ mkcommit a
+  $ mkcommit b
+  $ mkcommit c
+  $ hg prev
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  [7c3bad] add b
+  $ echo 'new b' > b
+  $ hg amend a -m 'Unchanged manifest, but dirty workdir'
+  warning: the changeset's children were left behind
+  (use 'hg restack' to rebase them)
+
+Test auto-restack heuristics - no changes to manifest but no children
+  $ reset
+  $ mkcommit a
+  $ mkcommit b
+  $ hg amend -m 'Unchanged manifest for b'
diff --git a/tests/test-fbamend-userestack.t b/tests/test-fbamend-userestack.t
--- a/tests/test-fbamend-userestack.t
+++ b/tests/test-fbamend-userestack.t
@@ -35,7 +35,7 @@
   $ mkcommit d
   $ hg up 1
   0 files updated, 0 files merged, 2 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg book
diff --git a/tests/test-smartlog-inhibit.t b/tests/test-smartlog-inhibit.t
--- a/tests/test-smartlog-inhibit.t
+++ b/tests/test-smartlog-inhibit.t
@@ -15,7 +15,7 @@
   $ hg book -r 3 test
   $ hg up 1
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  $ hg amend -m "amended"
+  $ hg amend -m "amended" --no-rebase
   warning: the changeset's children were left behind
   (use 'hg restack' to rebase them)
   $ hg smartlog -T '{rev} {bookmarks}'