diff --git a/git_rebase_update.py b/git_rebase_update.py
index 912004bc44..716111e209 100755
--- a/git_rebase_update.py
+++ b/git_rebase_update.py
@@ -256,9 +256,12 @@ def main(args=None):
   return_branch, return_workdir = find_return_branch_workdir()
   os.chdir(git.run('rev-parse', '--show-toplevel'))
 
-  if git.run('status', '--porcelain'):
-    print('Cannot rebase-update with uncommitted changes.')
-    return 1
+  if git.current_branch() == 'HEAD':
+    if git.run('status', '--porcelain'):
+      print('Cannot rebase-update with detached head + uncommitted changes.')
+      return 1
+  else:
+    git.freeze()  # just in case there are any local changes.
 
   branches_to_rebase = set(opts.branches)
   if opts.current:
@@ -319,6 +322,7 @@ def main(args=None):
     # return_branch may not be there any more.
     if return_branch in git.branches():
       git.run('checkout', return_branch)
+      git.thaw()
     else:
       root_branch = git.root()
       if return_branch != 'HEAD':
diff --git a/tests/git_rebase_update_test.py b/tests/git_rebase_update_test.py
index cc49928fd4..5df56b3d16 100755
--- a/tests/git_rebase_update_test.py
+++ b/tests/git_rebase_update_test.py
@@ -105,10 +105,6 @@ class GitRebaseUpdateTest(git_test_utils.GitRepoReadWriteTestBase):
     self.repo.git('reset', '--hard', self.repo['A'])
     with self.repo.open('old_file', 'w') as f:
       f.write('old_files we want to keep around')
-
-    output, _ = self.repo.capture_stdio(self.reup.main)
-    self.assertIn('Cannot rebase-update', output)
-
     self.repo.git('add', 'old_file')
     self.repo.git_commit('old_file')
     self.repo.git('config', 'branch.old_branch.dormant', 'true')
@@ -125,6 +121,12 @@ class GitRebaseUpdateTest(git_test_utils.GitRepoReadWriteTestBase):
     self.assertEqual(self.repo['A'], self.origin['A'])
     self.assertEqual(self.repo['E'], self.origin['E'])
 
+    with self.repo.open('bob', 'wb') as f:
+      f.write(b'testing auto-freeze/thaw')
+
+    output, _ = self.repo.capture_stdio(self.reup.main)
+    self.assertIn('Cannot rebase-update', output)
+
     self.repo.run(self.nb.main, ['empty_branch'])
     self.repo.run(self.nb.main, ['--upstream-current', 'empty_branch2'])
 
@@ -158,6 +160,11 @@ class GitRebaseUpdateTest(git_test_utils.GitRepoReadWriteTestBase):
     self.assertIn('foobar up-to-date', output)
     self.assertIn('sub_K up-to-date', output)
 
+    with self.repo.open('bob') as f:
+      self.assertEqual(b'testing auto-freeze/thaw', f.read())
+
+    self.assertEqual(self.repo.git('status', '--porcelain').stdout, '?? bob\n')
+
     self.repo.git('checkout', 'origin/main')
     _, err = self.repo.capture_stdio(self.rp.main, [])
     self.assertIn('Must specify new parent somehow', err)
@@ -186,6 +193,7 @@ class GitRebaseUpdateTest(git_test_utils.GitRepoReadWriteTestBase):
     self.assertTrue(self.repo.run(self.gc.in_rebase))
 
     self.repo.git('rebase', '--abort')
+    self.assertIsNone(self.repo.run(self.gc.thaw))
 
     self.assertSchema("""
     A B C D E F G M N O foobar1 foobar2 H I J K L
@@ -194,6 +202,8 @@ class GitRebaseUpdateTest(git_test_utils.GitRepoReadWriteTestBase):
                                               K sub_K
     """)
 
+    self.assertEqual(self.repo.git('status', '--porcelain').stdout, '?? bob\n')
+
     branches = self.repo.run(set, self.gc.branches())
     self.assertEqual(branches, {'branch_K', 'main', 'sub_K', 'root_A',
                                 'branch_L', 'old_branch', 'foobar',
@@ -304,6 +314,7 @@ class GitRebaseUpdateTest(git_test_utils.GitRepoReadWriteTestBase):
     self.assertIn('could not be cleanly rebased:', output)
     self.assertIn('  branch_K', output)
 
+
   def testTrackTag(self):
     self.origin.git('tag', 'lkgr', self.origin['M'])
     self.repo.git('tag', 'lkgr', self.repo['D'])