diff --git a/AGENTS.md b/AGENTS.md
index 7d4dbd9..cfed77d 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -162,7 +162,7 @@ the PR. Then add the `ready-to-merge` label. The auto-merge workflow will:
 1. **Validate** PR title format (`DEVX-N: <vikunja task title>`) and match against Vikunja task title
 2. **Check** that at least one substantive APPROVE review exists
 3. Wait for all CI checks to pass (including the `pr-review` job)
-4. Squash-merge with title: `DEVX-N <conventional commit message>` (space-separated, no colon after DEVX-N)
+4. Squash-merge with title: `DEVX-N: <conventional commit message>`
 5. The post-merge workflow marks the Vikunja task as done
 6. The release workflow automatically versions, tags, and publishes
 
@@ -259,7 +259,7 @@ by `python -m devx.tools.install_tools` and configured by
 
 ### git-cliff Commit Preprocessing
 
-Merge commits on master have the format `DEVX-N <conventional commit>`. The
+Merge commits on master have the format `DEVX-N: <conventional commit>`. The
 `cliff.toml` includes a `commit_preprocessors` entry that strips the `DEVX-N `
 prefix before parsing. This ensures all merged work appears in the changelog.
 
@@ -282,7 +282,7 @@ setuptools via `dynamic = ["version"]` in `pyproject.toml`.
 | Branch name | `DEVX-N-short-description` | `DEVX-12-add-release-script` |
 | Branch commits | `<conventional commit>` | `feat: add release script` |
 | PR title | `DEVX-N: <vikunja task title>` | `DEVX-12: Add release automation` |
-| Merge commit | `DEVX-N <conventional commit>` | `DEVX-12 feat: add release script` |
+| Merge commit | `DEVX-N: <conventional commit>` | `DEVX-12: feat: add release script` |
 
 ### Task ID Resolution
 
diff --git a/src/devx/ci/auto_merge.py b/src/devx/ci/auto_merge.py
index 893a7fc..1ecc218 100644
--- a/src/devx/ci/auto_merge.py
+++ b/src/devx/ci/auto_merge.py
@@ -226,12 +226,12 @@ def main(branch: str, pr_title: str, repo: str, pr_number: str) -> None:
     validate_pr_title(pr_title, task_id)
     validate_pr_title_matches_vikunja(pr_title, task_id)
 
-    # Build merge title: DEVX-N <conventional commit message> (space-separated, no colon)
+    # Build merge title: DEVX-N: <conventional commit message>
     commits = client.get_pr_commits(pr_num)
     conv_msg = extract_conventional_msg(commits)
     if not conv_msg:
         raise click.ClickException(_("Could not extract conventional commit message from PR commits."))
-    merge_title = f"{task_id} {conv_msg}"
+    merge_title = f"{task_id}: {conv_msg}"
 
     try:
         client.merge_pr(pr_num, merge_title)
diff --git a/tests/unit/test_auto_merge.py b/tests/unit/test_auto_merge.py
index 860887a..0e7a71d 100644
--- a/tests/unit/test_auto_merge.py
+++ b/tests/unit/test_auto_merge.py
@@ -221,7 +221,7 @@ class TestMain:
             ["DEVX-19-fix-bug", "DEVX-19: Fix timeout", "owner/repo", "7"],
         )
         assert result.exit_code == 0, result.output
-        mock_client.merge_pr.assert_called_once_with(7, "DEVX-19 fix: resolve timeout")
+        mock_client.merge_pr.assert_called_once_with(7, "DEVX-19: fix: resolve timeout")
 
     @patch.dict("os.environ", {"REPO_TOKEN": ""}, clear=True)
     def test_no_token_raises(self) -> None: