diff --git a/dist/index.js b/dist/index.js
index 9dddc47..323fbd1 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -5,7 +5,7 @@ const fs = require("fs");
 const path = require("path");
 class FallbackDirectoryResolverPlugin {
     constructor(options = {}) {
-        this.options = Object.assign(FallbackDirectoryResolverPlugin.defaultOptions, options);
+        this.options = Object.assign({}, FallbackDirectoryResolverPlugin.defaultOptions, options);
         this.pathRegex = new RegExp(this.options.getRegex(this.options.prefix));
         this.cache = {};
     }
diff --git a/src/index.ts b/src/index.ts
index fac7404..caa9dd6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -30,7 +30,7 @@ export class FallbackDirectoryResolverPlugin {
     private cache: { [key: string]: string | null };
 
     public constructor(options: IFallbackDirectoryResolverPluginOptions = {}) {
-        this.options = Object.assign(FallbackDirectoryResolverPlugin.defaultOptions, options);
+        this.options = Object.assign({}, FallbackDirectoryResolverPlugin.defaultOptions, options);
         this.pathRegex = new RegExp(this.options.getRegex(this.options.prefix));
         this.cache = {};
     }