diff --git a/src/localstorage.js b/src/localstorage.js
index b1dd3ab..da2f80d 100644
--- a/src/localstorage.js
+++ b/src/localstorage.js
@@ -1,26 +1,30 @@
 export class LocalStorage {
   constructor(jest) {
+    Object.defineProperty(this, 'store', {
+      enumerable: false,
+      value: {},
+    }),
     Object.defineProperty(this, 'getItem', {
       enumerable: false,
-      value: jest.fn(key => this[key] || null),
+      value: jest.fn(key => this.store[key] || null),
     });
     Object.defineProperty(this, 'setItem', {
       enumerable: false,
       // not mentioned in the spec, but we must always coerce to a string
       value: jest.fn((key, val = '') => {
-        this[key] = val + '';
+        this.store[key] = val + '';
       }),
     });
     Object.defineProperty(this, 'removeItem', {
       enumerable: false,
       value: jest.fn(key => {
-        delete this[key];
+        delete this.store[key];
       }),
     });
     Object.defineProperty(this, 'clear', {
       enumerable: false,
       value: jest.fn(() => {
-        Object.keys(this).map(key => delete this[key]);
+        Object.keys(this.store).map(key => delete this.store[key]);
       }),
     });
     Object.defineProperty(this, 'toString', {
@@ -31,15 +35,15 @@ export class LocalStorage {
     });
     Object.defineProperty(this, 'key', {
       enumerable: false,
-      value: jest.fn(idx => Object.keys(this)[idx] || null),
+      value: jest.fn(idx => Object.keys(this.store)[idx] || null),
     });
   } // end constructor
 
   get length() {
-    return Object.keys(this).length;
+    return Object.keys(this.store).length;
   }
   // for backwards compatibility
   get __STORE__() {
-    return this;
+    return this.store;
   }
 }