diff --git a/packages/webpack5/src/index.ts b/packages/webpack5/src/index.ts
index 93b466fd4e..c8765ec3ae 100644
--- a/packages/webpack5/src/index.ts
+++ b/packages/webpack5/src/index.ts
@@ -158,10 +158,10 @@ export function chainWebpack(
  * @param mergeFn An object or a function that optionally returns an object (can mutate the object directly and return nothing)
  */
 export function mergeWebpack(
-	mergeFn: (
+	mergeFn: ((
 		config: Partial<webpack.Configuration>,
 		env: IWebpackEnv,
-	) => any | Partial<webpack.Configuration>,
+	) => any) | Partial<webpack.Configuration>,
 ) {
 	webpackMerges.push(mergeFn);
 }