diff --git a/lib/webpack.js b/lib/webpack.js
index 8e621aabcac..82f0c754c1f 100644
--- a/lib/webpack.js
+++ b/lib/webpack.js
@@ -36,7 +36,7 @@ const getValidateSchema = memoize(() => require("./validateSchema"));
  */
 
 /**
- * @param {WebpackOptions[]} childOptions options array
+ * @param {ReadonlyArray<WebpackOptions>} childOptions options array
  * @param {MultiCompilerOptions} options options
  * @returns {MultiCompiler} a multi-compiler
  */
@@ -92,14 +92,14 @@ const createCompiler = rawOptions => {
 
 /**
  * @callback WebpackFunctionMulti
- * @param {WebpackOptions[] & MultiCompilerOptions} options options objects
+ * @param {ReadonlyArray<WebpackOptions> & MultiCompilerOptions} options options objects
  * @param {Callback<MultiStats>=} callback callback
  * @returns {MultiCompiler} the multi compiler object
  */
 
 const webpack = /** @type {WebpackFunctionSingle & WebpackFunctionMulti} */ (
 	/**
-	 * @param {WebpackOptions | (WebpackOptions[] & MultiCompilerOptions)} options options
+	 * @param {WebpackOptions | (ReadonlyArray<WebpackOptions> & MultiCompilerOptions)} options options
 	 * @param {Callback<Stats> & Callback<MultiStats>=} callback callback
 	 * @returns {Compiler | MultiCompiler}
 	 */
@@ -115,14 +115,18 @@ const webpack = /** @type {WebpackFunctionSingle & WebpackFunctionMulti} */ (
 			let watchOptions;
 			if (Array.isArray(options)) {
 				/** @type {MultiCompiler} */
-				compiler = createMultiCompiler(options, options);
+				compiler = createMultiCompiler(
+					options,
+					/** @type {MultiCompilerOptions} */ (options)
+				);
 				watch = options.some(options => options.watch);
 				watchOptions = options.map(options => options.watchOptions || {});
 			} else {
+				const webpackOptions = /** @type {WebpackOptions} */ (options);
 				/** @type {Compiler} */
-				compiler = createCompiler(options);
-				watch = options.watch;
-				watchOptions = options.watchOptions || {};
+				compiler = createCompiler(webpackOptions);
+				watch = webpackOptions.watch;
+				watchOptions = webpackOptions.watchOptions || {};
 			}
 			return { compiler, watch, watchOptions };
 		};
diff --git a/types.d.ts b/types.d.ts
index 98f700cdb7a..90a6ca18564 100644
--- a/types.d.ts
+++ b/types.d.ts
@@ -11925,14 +11925,14 @@ declare function exports(
 	callback?: CallbackWebpack<Stats>
 ): Compiler;
 declare function exports(
-	options: Configuration[] & MultiCompilerOptions,
+	options: ReadonlyArray<Configuration> & MultiCompilerOptions,
 	callback?: CallbackWebpack<MultiStats>
 ): MultiCompiler;
 declare namespace exports {
 	export const webpack: {
 		(options: Configuration, callback?: CallbackWebpack<Stats>): Compiler;
 		(
-			options: Configuration[] & MultiCompilerOptions,
+			options: ReadonlyArray<Configuration> & MultiCompilerOptions,
 			callback?: CallbackWebpack<MultiStats>
 		): MultiCompiler;
 	};