diff --git a/conventional_pre_commit/format.py b/conventional_pre_commit/format.py
index 5b7ec83..28a840a 100644
--- a/conventional_pre_commit/format.py
+++ b/conventional_pre_commit/format.py
@@ -74,7 +74,7 @@ def is_merge(self, commit_msg: str = ""):
         See the documentation, please https://git-scm.com/docs/git-merge.
         """
         commit_msg = self.clean(commit_msg)
-        return commit_msg.startswith("Merge branch ")
+        return commit_msg.lower().startswith("merge branch ")
 
 
 class ConventionalCommit(Commit):
diff --git a/tests/test_format.py b/tests/test_format.py
index 617f61a..a52b9bc 100644
--- a/tests/test_format.py
+++ b/tests/test_format.py
@@ -396,7 +396,7 @@ def test_has_autosquash_prefix(commit, input, expected_result):
     "input,expected_result",
     [
         ("Merge branch '2.x.x' into '1.x.x'", True),
-        ("Merge branch 'dev' into 'main'", True),
+        ("merge branch 'dev' into 'main'", True),
         ("nope not a merge commit", False),
         ("type: subject", False),
     ],