diff --git a/lib/karma-webpack.js b/lib/karma-webpack.js
index 8edcbfa..40f52e3 100644
--- a/lib/karma-webpack.js
+++ b/lib/karma-webpack.js
@@ -80,9 +80,19 @@ function preprocessorFactory(config, emitter) {
     controller.karmaEmitter = emitter;
   }
 
+  const transformPath =
+    config.webpack.transformPath ||
+    ((filepath) => {
+      // for *.js files by default
+      const info = path.parse(filepath);
+      return `${path.join(info.dir, info.name)}.js`;
+    });
+
   return async function processFile(content, file, done) {
     await controller.bundle();
 
+    file.path = transformPath(file.path); // eslint-disable-line no-param-reassign
+
     const bundleContent = controller.bundlesContent[path.parse(file.path).base];
     done(null, bundleContent);
   };