diff --git a/.npmignore b/.npmignore
index a8aad13..e9a1048 100644
--- a/.npmignore
+++ b/.npmignore
@@ -1,3 +1,5 @@
 coverage
 .idea
-node_modules
\ No newline at end of file
+node_modules
+.DS_Store
+test
\ No newline at end of file
diff --git a/README.md b/README.md
index 7493520..31e3177 100644
--- a/README.md
+++ b/README.md
@@ -7,6 +7,7 @@ This is a polyfill library for JavaScript's `URLSearchParams` class.
 * Implemented all features from [MDN document](https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams).
 * Can use for both browsers and Node.js.
 * Detect if browsers have full support for `URLSearchParams` and extend it
+* Compatible with IE8 and above
 
 
 ## Installation
diff --git a/index.js b/index.js
index d65cc8f..6af93a9 100644
--- a/index.js
+++ b/index.js
@@ -61,7 +61,7 @@
      *
      * @param {string} name
      */
-    prototype.delete = function(name) {
+    prototype['delete'] = function(name) {
         delete this [__URLSearchParams__] [name];
     };
 
@@ -171,7 +171,7 @@
         keys.sort();
 
         for (i = 0; i < keys.length; i++) {
-            this.delete(keys[i]);
+            this['delete'](keys[i]);
         }
         for (i = 0; i < keys.length; i++) {
             var key = keys[i], values = dict[key];
diff --git a/package.json b/package.json
index 92bbff8..cd06347 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "url-search-params-polyfill",
-  "version": "5.0.1",
+  "version": "5.1.0",
   "description": "a simple polyfill for javascript URLSearchParams",
   "homepage": "https://github.com/jerrybendy/url-search-params-polyfill",
   "main": "index.js",