diff --git a/build/tasks/compile-packages-slug-task.coffee b/build/tasks/compile-packages-slug-task.coffee
index 747b18713..fea76edda 100644
--- a/build/tasks/compile-packages-slug-task.coffee
+++ b/build/tasks/compile-packages-slug-task.coffee
@@ -47,7 +47,7 @@ module.exports = (grunt) ->
 
       for extension, paths of moduleCache.extensions
         if paths.length is 0
-          delete metadata._atomModuleCache?.extensions[extension]
+          delete moduleCache.extensions[extension]
 
     metadata = grunt.file.readJSON(path.join(appDir, 'package.json'))
     metadata._atomPackages = packages