diff --git a/.github/workflows/zephyr-4.x.yml b/.github/workflows/zephyr-4.x.yml
index ab023a8f42..1350947dc9 100644
--- a/.github/workflows/zephyr-4.x.yml
+++ b/.github/workflows/zephyr-4.x.yml
@@ -48,9 +48,11 @@ jobs:
         id: src
         run: |
           if [[ "${{ github.event_name }}" == "pull_request" ]]; then
-            # Fetch via upstream PR ref so renames, deletes, or visibility changes on the fork do not break us
+            # Fetch via upstream PR ref so renames, deletes, or visibility changes on the fork do not break us.
+            # Use the /merge ref (PR merged into the base branch) instead of /head so we test master+PR,
+            # picking up fixes already on master rather than testing the PR branch in isolation.
             echo "repo=https://github.com/${{ github.repository }}" >> "$GITHUB_OUTPUT"
-            echo "branch=refs/pull/${{ github.event.pull_request.number }}/head" >> "$GITHUB_OUTPUT"
+            echo "branch=refs/pull/${{ github.event.pull_request.number }}/merge" >> "$GITHUB_OUTPUT"
           else
             echo "repo=https://github.com/${{ github.repository }}" >> "$GITHUB_OUTPUT"
             echo "branch=${{ github.ref_name }}" >> "$GITHUB_OUTPUT"