diff --git a/hgext3rd/tweakdefaults.py b/hgext3rd/tweakdefaults.py
index e1ad58435e..2bc715d517 100644
--- a/hgext3rd/tweakdefaults.py
+++ b/hgext3rd/tweakdefaults.py
@@ -338,7 +338,7 @@ def update(orig, ui, repo, node=None, rev=None, **kwargs):
     # By default, never update when there are local changes unless updating to
     # the current rev. This is useful for, eg, arc feature when the only
     # thing changing is the bookmark.
-    if not kwargs['clean'] and not kwargs['nocheck']:
+    if not kwargs['clean'] and not kwargs['nocheck'] and not kwargs['merge']:
         target = node or rev
         if target and scmutil.revsingle(repo, target, target).rev() != \
                 repo.revs('.').first():
diff --git a/tests/test-tweakdefaults-update.t b/tests/test-tweakdefaults-update.t
new file mode 100644
index 0000000000..d4e944899c
--- /dev/null
+++ b/tests/test-tweakdefaults-update.t
@@ -0,0 +1,74 @@
+  $ extpath=`dirname $TESTDIR`
+  $ cp $extpath/hgext3rd/tweakdefaults.py $TESTTMP # use $TESTTMP substitution in message
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > tweakdefaults=$TESTTMP/tweakdefaults.py
+  > rebase=
+  > EOF
+
+Set up the repository.
+  $ hg init repo
+  $ cd repo
+  $ hg debugbuilddag -m '+4 *3 +1'
+  $ hg log --graph -r 0:: -T '{rev}'
+  o  5
+  |
+  o  4
+  |
+  | o  3
+  | |
+  | o  2
+  |/
+  o  1
+  |
+  o  0
+  
+  $ hg up 3
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+Make an uncommitted change.
+  $ echo foo > foo
+  $ hg add foo
+  $ hg st
+  A foo
+
+Can always update to current commit.
+  $ hg up .
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+By default, --check should be set.
+  $ hg up 2
+  abort: uncommitted changes
+  [255]
+  $ hg up --nocheck 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+Updates to other branches should fail without --merge.
+  $ hg up 4
+  abort: uncommitted changes
+  [255]
+  $ hg up --nocheck 4
+  abort: uncommitted changes
+  (commit or update --clean to discard changes)
+  [255]
+  $ hg up --merge 4
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+Certain flags shouldn't work together.
+  $ hg up --check --merge 3
+  abort: can only specify one of -C/--clean, -c/--check, or -m/merge
+  [255]
+  $ hg up --check --clean 3
+  abort: can only specify one of -C/--clean, -c/--check, or -m/merge
+  [255]
+  $ hg up --clean --merge 3
+  abort: can only specify one of -C/--clean, -c/--check, or -m/merge
+  [255]
+
+--clean should work as expected.
+  $ hg st
+  A foo
+  $ hg up --clean 3
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg st
+  ? foo