diff --git a/src/node/MonkeyPlugin.ts b/src/node/MonkeyPlugin.ts
index f2b3de3..dcae4ae 100644
--- a/src/node/MonkeyPlugin.ts
+++ b/src/node/MonkeyPlugin.ts
@@ -746,7 +746,7 @@ export class MonkeyPlugin {
 
   resolveExternals(
     data: ExternalItemFunctionData,
-    callback: (err?: Error, result?: ExternalItemValue) => void,
+    callback: (err?: Error | null, result?: ExternalItemValue) => void,
     userDefinedExternals?:
       | Record<string, ExternalItemValue>
       | ExtractFunction<Configuration["externals"]>