diff --git a/.github/workflows/shellcheck.yml b/.github/workflows/shellcheck.yml
index 5272881..8be950c 100644
--- a/.github/workflows/shellcheck.yml
+++ b/.github/workflows/shellcheck.yml
@@ -20,7 +20,10 @@ jobs:
 
       - name: Run ShellCheck on all shell scripts
         run: |
-          shellcheck pre-commit commit-msg pre-push post-checkout post-commit post-merge install.sh uninstall.sh test/install_test.sh
+          shellcheck pre-commit commit-msg pre-push post-checkout post-commit post-merge install.sh uninstall.sh test/install_test.sh test/commit_msg_test.sh
 
       - name: Run install script regression tests
         run: bash test/install_test.sh
+
+      - name: Run commit message regression tests
+        run: bash test/commit_msg_test.sh
diff --git a/test/commit_msg_test.sh b/test/commit_msg_test.sh
new file mode 100644
index 0000000..349a767
--- /dev/null
+++ b/test/commit_msg_test.sh
@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "$0")/.." && pwd)"
+commit_msg_hook="$repo_root/commit-msg"
+tmpdir="$(mktemp -d)"
+trap 'rm -rf "$tmpdir"' EXIT
+
+run_hook() {
+	local expected_status="$1"
+	local message="$2"
+	local msg_file="$tmpdir/message"
+
+	printf '%s\n' "$message" > "$msg_file"
+
+	set +e
+	output=$(bash "$commit_msg_hook" "$msg_file" 2>&1)
+	status=$?
+	set -e
+
+	if [ "$status" -ne "$expected_status" ]; then
+		echo "expected exit $expected_status for message: $message" >&2
+		echo "got exit $status" >&2
+		echo "$output" >&2
+		exit 1
+	fi
+}
+
+assert_rejected() {
+	local message="$1"
+
+	run_hook 1 "$message"
+	if ! printf '%s' "$output" | grep -Fq "ERROR: Commit message does not follow Conventional Commits format."; then
+		echo "expected rejection output for message: $message" >&2
+		echo "$output" >&2
+		exit 1
+	fi
+}
+
+run_hook 0 "feat: add checkout hook"
+run_hook 0 "fix(shell/hooks): preserve lfs args"
+run_hook 0 "feat(api)!: change hook contract"
+run_hook 0 "Merge pull request #6 from taigrr/cd/clear-conflicting-hook-config"
+run_hook 0 "fixup! fix(shell): preserve lfs args"
+run_hook 0 "squash! test(shell): add regression coverage"
+
+assert_rejected "update hook behavior"
+assert_rejected "feature: add checkout hook"
+assert_rejected "fix(shell):"
+
+echo "commit-msg regression tests passed"