diff --git a/packages/core/package.json b/packages/core/package.json
index 266ae7f999e..5ff43014f60 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -22,9 +22,9 @@
 		"test": "tslint 'src/**/*.ts' && jest -w 1 --coverage",
 		"build-with-test": "npm test && npm run build",
 		"build:cjs": "node ./build es5 && webpack && webpack --config ./webpack.config.dev.js",
-		"build:esm": "node ./build es6",
+		"build:esm": "rimraf lib-esm && node ./build es6",
 		"build:cjs:watch": "node ./build es5 --watch",
-		"build:esm:watch": "node ./build es6 --watch",
+		"build:esm:watch": "rimraf lib-esm && node ./build es6 --watch",
 		"build": "npm run clean && npm run generate-version && npm run build:esm && npm run build:cjs",
 		"generate-version": "genversion src/Platform/version.ts --es6 --semi",
 		"clean": "rimraf lib-esm lib dist",