diff --git a/.github/workflows/cron_iwyu.yml b/.github/workflows/cron_iwyu.yml
index 9628bc1..d6810c9 100644
--- a/.github/workflows/cron_iwyu.yml
+++ b/.github/workflows/cron_iwyu.yml
@@ -32,6 +32,7 @@ jobs:
         uses: seqan/actions/iwyu@main
         with:
           configure_path: .
+          additional_mapping: .github/config/custom.imp
           token: ${{ secrets.SEQAN_ACTIONS_PAT }}
           gpg_key: ${{ secrets.SEQAN_ACTIONS_GPG_KEY }}
           gpg_passphrase: ${{ secrets.SEQAN_ACTIONS_GPG_PASSPHRASE }}