diff --git a/.github/workflows/build-docker.yml b/.github/workflows/build-docker.yml
index b6ee7f466..3cb5b17d7 100644
--- a/.github/workflows/build-docker.yml
+++ b/.github/workflows/build-docker.yml
@@ -60,12 +60,14 @@ jobs:
                   then
                       # If we're in a PR, build the container from the fork's source.
                       INVEST_REPO="${{ github.event.pull_request.head.repo.full_name }}"
+                      INVEST_VERSION="${{ github.event.pull_request.merge_commit_sha }}"
                   else
                       INVEST_REPO="${{ github.repository }}"
+                      INVEST_VERSION="${{ github.sha }}"
                   fi
                   cd docker && docker build \
                         --build-arg="INVEST_REPO=${INVEST_REPO}" \
-                        --build-arg="INVEST_VERSION=${{ github.sha }}" \
+                        --build-arg="INVEST_VERSION=${INVEST_VERSION}" \
                         -t ghcr.io/${{ github.repository_owner }}/${{ env.CONTAINER_NAME }}:latest \
                         -t ghcr.io/${{ github.repository_owner }}/${{ env.CONTAINER_NAME }}:${{ github.sha }} \
                         -t ghcr.io/${{ github.repository_owner }}/${{ env.CONTAINER_NAME }}:${SANITIZED_REF} \