diff --git a/packages/angular_devkit/build_angular/src/angular-cli-files/plugins/karma.ts b/packages/angular_devkit/build_angular/src/angular-cli-files/plugins/karma.ts
index 71060d02a597..92f4776ae7b6 100644
--- a/packages/angular_devkit/build_angular/src/angular-cli-files/plugins/karma.ts
+++ b/packages/angular_devkit/build_angular/src/angular-cli-files/plugins/karma.ts
@@ -144,6 +144,7 @@ const init: any = (config: any, emitter: any, customFileHandlers: any) => {
   // Files need to be served from a custom path for Karma.
   webpackConfig.output.path = '/_karma_webpack_/';
   webpackConfig.output.publicPath = '/_karma_webpack_/';
+  webpackConfig.output.devtoolModuleFilenameTemplate = '[namespace]/[resource-path]?[loaders]';
 
   let compiler: any;
   try {