diff --git a/packages/babel-core/src/util.js b/packages/babel-core/src/util.js
index 0ee5e62a96..4da7503e8c 100644
--- a/packages/babel-core/src/util.js
+++ b/packages/babel-core/src/util.js
@@ -116,7 +116,7 @@ export function shouldIgnore(
   ignore: Array<RegExp | Function> = [],
   only?: Array<RegExp | Function>,
 ): boolean {
-  filename = slash(filename);
+  filename = filename.replace(/\\/g, "/");
 
   if (only) {
     for (let pattern of only) {