diff --git a/index.d.ts b/index.d.ts
index 53f5ae3..125d0c4 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -8,7 +8,7 @@ export interface Options {
 	 * will be used
 	 * @default ['module', 'main']
 	 */
-	mainFields?: string[];
+	mainFields?: ReadonlyArray<string>;
 
 	/**
 	 * @deprecated use "mainFields" instead
diff --git a/typings-test.js b/typings-test.js
index 2175718..a956b60 100644
--- a/typings-test.js
+++ b/typings-test.js
@@ -11,6 +11,7 @@ const config = {
 	},
 	plugins: [
 		resolve({
+			mainFields: ['untranspiled', 'module', 'main'],
 			module: true,
 			jsnext: true,
 			main: true,
@@ -19,6 +20,7 @@ const config = {
 			preferBuiltins: false,
 			jail: '/my/jail/path',
 			only: [ 'some_module', /^@some_scope\/.*$/ ],
+			dedupe: ['lodash'],
 			modulesOnly: true,
 			customResolveOptions: {
 				moduleDirectory: 'js_modules'