diff --git a/lib/build/bundle.js b/lib/build/bundle.js
index 935e7e6e3..3e0b7383c 100644
--- a/lib/build/bundle.js
+++ b/lib/build/bundle.js
@@ -243,7 +243,7 @@ exports.Bundle = class {
 
     return work.then(() => {
       const Concat = require('concat-with-sourcemaps');
-      let concat = new Concat(true, this.config.name, os.EOL);
+      let concat = new Concat(true, this.config.name, ';' + os.EOL);
       const generateHashedPath = require('./utils').generateHashedPath;
       const generateHash = require('./utils').generateHash;
       let needsSourceMap = false;