diff --git a/build/lib/compilation.ts b/build/lib/compilation.ts
index 2cc04d2c977..9029c6231ed 100644
--- a/build/lib/compilation.ts
+++ b/build/lib/compilation.ts
@@ -128,3 +128,3 @@ export function compileTask(src: string, out: string, build: boolean): () => Nod
 			mangleStream = es.through(function write(data: File) {
-				const newContents = newContentsByFileName.get(data.path);
+				const newContents = newContentsByFileName.get(data.path.replace(/\\/g, '/'));
 				if (newContents !== undefined) {