diff --git a/modules/utils/rewriteBareModuleIdentifiers.js b/modules/utils/rewriteBareModuleIdentifiers.js
index be9fbcc..dc51a69 100644
--- a/modules/utils/rewriteBareModuleIdentifiers.js
+++ b/modules/utils/rewriteBareModuleIdentifiers.js
@@ -20,7 +20,7 @@ export default function rewriteBareModuleIdentifiers(code, packageConfig) {
     // from the original file. This ensures minified
     // .mjs stays minified; see #149
     retainLines: true,
-    plugins: [unpkgRewrite(origin, dependencies)]
+    plugins: [unpkgRewrite(origin, dependencies), "@babel/plugin-proposal-optional-chaining"]
   };
 
   return babel.transform(code, options).code;
diff --git a/package.json b/package.json
index 1806dc2..771db86 100644
--- a/package.json
+++ b/package.json
@@ -13,6 +13,7 @@
   "dependencies": {
     "@babel/core": "^7.2.2",
     "@babel/plugin-proposal-class-properties": "^7.2.3",
+    "@babel/plugin-proposal-optional-chaining": "^7.12.7",
     "@babel/plugin-syntax-dynamic-import": "^7.2.0",
     "@babel/plugin-syntax-export-default-from": "^7.2.0",
     "@babel/plugin-syntax-export-namespace-from": "^7.2.0",