diff --git a/experimental/babel-preset-env/src/index.js b/experimental/babel-preset-env/src/index.js
index 5400dad9ff..b1c8842094 100644
--- a/experimental/babel-preset-env/src/index.js
+++ b/experimental/babel-preset-env/src/index.js
@@ -243,7 +243,10 @@ export default function buildPreset(context, opts = {}) {
   );
 
   if (useBuiltIns === true) {
-    plugins.push([addUsedBuiltInsPlugin, { polyfills, regenerator, debug }]);
+    plugins.push([
+      addUsedBuiltInsPlugin,
+      { polyfills: new Set(polyfills), regenerator, debug },
+    ]);
   } else if (useBuiltIns === "entry") {
     plugins.push([useBuiltInsEntryPlugin, { polyfills, regenerator }]);
   }
diff --git a/experimental/babel-preset-env/src/use-built-ins-plugin.js b/experimental/babel-preset-env/src/use-built-ins-plugin.js
index 6861264fc4..c4f7a3b7fa 100644
--- a/experimental/babel-preset-env/src/use-built-ins-plugin.js
+++ b/experimental/babel-preset-env/src/use-built-ins-plugin.js
@@ -38,12 +38,12 @@ export default function({ types: t }) {
   function addUnsupported(path, polyfills, builtIn, builtIns) {
     if (Array.isArray(builtIn)) {
       for (const i of builtIn) {
-        if (polyfills.indexOf(i) !== -1) {
+        if (polyfills.has(i)) {
           addImport(path, `core-js/modules/${i}`, builtIns);
         }
       }
     } else {
-      if (polyfills.indexOf(builtIn) !== -1) {
+      if (polyfills.has(builtIn)) {
         addImport(path, `core-js/modules/${builtIn}`, builtIns);
       }
     }