diff --git a/.github/workflows/bundle-size.yml b/.github/workflows/bundle-size.yml
index d6ab4015b..1a5feb070 100644
--- a/.github/workflows/bundle-size.yml
+++ b/.github/workflows/bundle-size.yml
@@ -34,6 +34,10 @@ jobs:
             - name: Compressed Size Diff
               uses: preactjs/compressed-size-action@66325aad6443cb7cf89c4bfcd414aea2367cda94 # v3
               with:
+                  # Force npm — the action defaults to pnpm when both
+                  # package-lock.json and pnpm-lock.yaml exist, but this
+                  # project is npm-managed (see package.json scripts).
+                  install-script: 'npm ci'
                   build-script: 'build'
                   pattern: 'packages/frontend/dist/**/*.{js,css}'
                   strip-hash: '\\b\\w{8}\\.'