diff --git a/.github/workflows/update-toolchain.yml b/.github/workflows/update-toolchain.yml
index 364150305..7e85cbc4a 100644
--- a/.github/workflows/update-toolchain.yml
+++ b/.github/workflows/update-toolchain.yml
@@ -14,6 +14,7 @@ jobs:
       - name: checkout
         uses: actions/checkout@v6
         with:
+          ref: nightly-testing
           fetch-depth: 0
 
       - name: install jq
@@ -22,7 +23,7 @@ jobs:
       - name: get toolchain tags
         id: toolchain-tag
         run: |
-          REPO_TAG=$(sed 's/.*://1' lean-toolchain | tr -d '\n')
+          REPO_TAG=$(git show main:lean-toolchain | cut -d':' -f2 | tr -d '\n')
           LEAN_TAG=$(curl -s "https://api.github.com/repos/leanprover/lean4/releases" | jq -r '.[0].tag_name' | tr -d '\n')
           echo "repo_tag=$REPO_TAG" >> $GITHUB_OUTPUT
           echo "lean_tag=$LEAN_TAG" >> $GITHUB_OUTPUT
@@ -32,8 +33,7 @@ jobs:
         if: ${{ steps.toolchain-tag.outputs.lean_tag != steps.toolchain-tag.outputs.repo_tag }}
         run: |
           git config user.name "${{ github.actor }}"
-          git config user.email "${{ github.actor_id}}+${{ github.actor }}@users.noreply.github.com"
-          git merge -X theirs origin/nightly-testing
+          git config user.email "${{ github.actor_id }}+${{ github.actor }}@users.noreply.github.com"
           echo "leanprover/lean4:${{ steps.toolchain-tag.outputs.lean_tag }}" > lean-toolchain
 
       - name: create pull request
@@ -42,5 +42,6 @@ jobs:
           token: ${{ secrets.UNICODE_BASIC_TOKEN }}
           commit-message: "chore: update toolchain ${{ steps.toolchain-tag.outputs.lean_tag }}"
           branch: update-toolchain-${{ steps.toolchain-tag.outputs.lean_tag }}
+          base: main
           delete-branch: true
           title: "chore: update toolchain ${{ steps.toolchain-tag.outputs.lean_tag }}"