diff --git a/index.js b/index.js
index cda3576..c76de68 100644
--- a/index.js
+++ b/index.js
@@ -169,7 +169,7 @@ GeneratePackageJsonPlugin.prototype.apply = function (compiler) {
   const computePackageJson = (compilation) => {
     const dependencyTypes = ["dependencies", "devDependencies", "peerDependencies"]
 
-    const modules = Object.assign({}, this.additionalDependencies);
+    const modules = {};
 
     const getInstalledVersionForModuleName = (moduleName, context) => {
       let modulePackageFile;
@@ -344,6 +344,8 @@ GeneratePackageJsonPlugin.prototype.apply = function (compiler) {
       }
     }
 
+    Object.assign(modules, this.additionalDependencies);
+
     logIfDebug(`GPJWP: Modules to be used in generated package.json`, modules);
 
     const finalPackageValues = Object.assign({}, basePackageValues, { dependencies: orderKeys(modules) });