diff --git a/.github/workflows/build-test.yml b/.github/workflows/build-test.yml
index 7bef8686..b69c5095 100644
--- a/.github/workflows/build-test.yml
+++ b/.github/workflows/build-test.yml
@@ -60,7 +60,7 @@ jobs:
         with:
           node-version-file: '.nvmrc'
           cache: 'yarn'
-      - run: yarn
+      - run: yarn --immutable
       - run: yarn test
       - name: Require clean working directory
         shell: bash