diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 6fa16b18..f0791f32 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -31,6 +31,19 @@ jobs:
       - name: Build
         run: npm run all
 
+      - name: Check dist/ is up to date
+        run: |
+          if ! git diff --quiet dist/; then
+            echo "::warning::dist/ is out of date. Run 'npm run package' locally and commit the result."
+            git diff --stat dist/
+            echo "## dist/ is out of date" >> $GITHUB_STEP_SUMMARY
+            echo "Run \`npm run package\` locally and commit the result." >> $GITHUB_STEP_SUMMARY
+            echo "" >> $GITHUB_STEP_SUMMARY
+            echo "\`\`\`" >> $GITHUB_STEP_SUMMARY
+            git diff --stat dist/ >> $GITHUB_STEP_SUMMARY
+            echo "\`\`\`" >> $GITHUB_STEP_SUMMARY
+          fi
+
   test:
     name: Test
     runs-on: ubuntu-latest