diff --git a/.github/workflows/doctest.yml b/.github/workflows/doctest.yml
new file mode 100644
index 0000000..6657d2b
--- /dev/null
+++ b/.github/workflows/doctest.yml
@@ -0,0 +1,21 @@
+name: Run doctests
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Set up Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: '3.9'
+
+    - name: Install package
+      run: pip install .
+
+    - name: Run tests
+      run: python -m doctest riot_release_manager.py
diff --git a/riot_release_manager.py b/riot_release_manager.py
index 8c9dace..1990550 100755
--- a/riot_release_manager.py
+++ b/riot_release_manager.py
@@ -123,10 +123,32 @@ def update_branch(repo_dir, remote, branch):
         stderr=subprocess.DEVNULL
     )
 
+
+def _merge_commits_to_prs(log: str):
+    """Extracts PR numbers from merge commits in a git log.
+
+    Args:
+        log: git log
+
+    Returns:
+        list of PR numbers
+
+    >>> log = 'Merge #19495\\n'
+    >>> log += 'drivers/lsm303agr: Rename deprecated unit G to GForce\\n'
+    >>> log += 'Merge #19499 #19500\\n'
+    >>> log += 'sam0/usbdev: partial revert of #17086\\n'
+    >>> prs = _merge_commits_to_prs(log)
+    >>> assert prs == [19495, 19499, 19500]
+    """
+    merge_lines = [line for line in log.splitlines() if line.strip().startswith('Merge #')]
+    return [int(line) for line in re.findall(r"#([0-9]+)", '\n'.join(merge_lines))]
+
+
 def get_merged_prs_with_git(repo_dir, since):
     log = subprocess.run(git(repo_dir) + ["log", "--merges", "%s..HEAD" % since],
                          capture_output=True, text=True).stdout
-    return [int(line) for line in re.findall(r"Merge pull request #([0-9]+) from", log)]
+    return _merge_commits_to_prs(log)
+
 
 def get_tags(repo_dir, remote):
     subprocess.run(git(repo_dir) + ["fetch", "--tags", remote])