diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 7f9b40f..0fd5249 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -15,7 +15,8 @@ jobs:
       with:
         node-version: 10.x
 
-    - uses: actions/cache@v2
+    - name: Yarn cache
+      uses: actions/cache@v2
       with:
         path: .yarn/cache
         key: yarn-${{ hashFiles('yarn.lock') }}
diff --git a/build.js b/build.js
index 1f1c899..f0b9e65 100755
--- a/build.js
+++ b/build.js
@@ -38,9 +38,13 @@ const compiler = webpack({
     extensions: [`.mjs`, `.js`, `.ts`, `.tsx`, `.json`],
   },
 
-  externals: Object.fromEntries(
-    EXTERNALS.map((name) => [name, `commonjs ${name}`])
-  ),
+  externals: (() => {
+    const res = {};
+    for (const name of EXTERNALS) {
+      res[name] = `commonjs ${name}`;
+    }
+    return res;
+  })(),
 
   module: {
     rules: [