diff --git a/pre_commit/commands/autoupdate.py b/pre_commit/commands/autoupdate.py
index 5e804c14..05187b85 100644
--- a/pre_commit/commands/autoupdate.py
+++ b/pre_commit/commands/autoupdate.py
@@ -108,7 +108,9 @@ def _write_new_config(path, rev_infos):
         new_rev_s = ordered_dump({'rev': rev_info.rev}, **C.YAML_DUMP_KWARGS)
         new_rev = new_rev_s.split(':', 1)[1].strip()
         if rev_info.frozen is not None:
-            comment = '  # {}'.format(rev_info.frozen)
+            comment = '  # frozen: {}'.format(rev_info.frozen)
+        elif match.group(4).strip().startswith('# frozen:'):
+            comment = ''
         else:
             comment = match.group(4)
         lines[idx] = REV_LINE_FMT.format(
diff --git a/tests/commands/autoupdate_test.py b/tests/commands/autoupdate_test.py
index 9a725588..f8ea084e 100644
--- a/tests/commands/autoupdate_test.py
+++ b/tests/commands/autoupdate_test.py
@@ -312,9 +312,14 @@ def test_autoupdate_freeze(tagged, in_tmpdir, store):
 
     assert autoupdate(C.CONFIG_FILE, store, freeze=True, tags_only=False) == 0
     with open(C.CONFIG_FILE) as f:
-        expected = 'rev: {}  # v1.2.3'.format(tagged.head_rev)
+        expected = 'rev: {}  # frozen: v1.2.3'.format(tagged.head_rev)
         assert expected in f.read()
 
+    # if we un-freeze it should remove the frozen comment
+    assert autoupdate(C.CONFIG_FILE, store, freeze=False, tags_only=False) == 0
+    with open(C.CONFIG_FILE) as f:
+        assert 'rev: v1.2.3\n' in f.read()
+
 
 def test_autoupdate_tags_only(tagged, in_tmpdir, store):
     # add some commits after the tag