diff --git a/src/utils.js b/src/utils.js
index d5816047..2e267baa 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -1,15 +1,5 @@
 import semver from 'semver';
 
-/*
- * Implementation of String.endsWith, which errors in node.
- *
- */
-export function endsWith(string, suffix) {
-  string = String(string);
-  suffix = String(suffix);
-  return string.indexOf(suffix, string.length - suffix.length) !== -1;
-}
-
 /*
  * Template tag for removing whitespace and new lines
  * in order to be able to use multiline template strings
diff --git a/src/xpi.js b/src/xpi.js
index dd577116..8e42a916 100644
--- a/src/xpi.js
+++ b/src/xpi.js
@@ -1,7 +1,6 @@
 import yauzl from 'yauzl';
 
 import { DuplicateZipEntryError } from 'exceptions';
-import { endsWith } from 'utils';
 
 
 /*
@@ -131,7 +130,7 @@ export default class Xpi {
           let files = [];
 
           for (let filename in metadata) {
-            if (endsWith(filename, ext)) {
+            if (filename.endsWith(ext)) {
               files.push(filename);
             }
           }
diff --git a/tests/test.utils.js b/tests/test.utils.js
index 134d606e..d0a16d65 100644
--- a/tests/test.utils.js
+++ b/tests/test.utils.js
@@ -1,31 +1,6 @@
 import * as utils from 'utils';
 
 
-describe('utils.endsWith()', function() {
-
-  it('returns true if a string ends with a specified string', () => {
-    assert.ok(utils.endsWith('Matthew', 'ew'));
-  });
-
-  it('returns false if a string does not end with a specified string', () => {
-    assert.notOk(utils.endsWith('Matthew', 'Mac'));
-  });
-
-  it('returns true if a string ends with itself', () => {
-    assert.ok(utils.endsWith('Matthew', 'Matthew'));
-  });
-
-  it('returns true if a strange character is present', () => {
-    assert.ok(utils.endsWith('G chord! 🎸', '🎸'));
-  });
-
-  it("casts to strings if strings aren't used", () => {
-    assert.ok(utils.endsWith(222, '22'));
-    assert.ok(utils.endsWith('Hello!!11', 11));
-  });
-});
-
-
 describe('utils.singleLineString()', function() {
 
   it('reduce a multiline template string into one string', () => {
diff --git a/tests/test.xpi.js b/tests/test.xpi.js
index 71abd709..41da6b8e 100644
--- a/tests/test.xpi.js
+++ b/tests/test.xpi.js
@@ -1,6 +1,5 @@
 import { Readable } from 'stream';
 
-import { endsWith } from 'utils';
 import Xpi from 'xpi';
 import { DEFLATE_COMPRESSION, NO_COMPRESSION } from 'const';
 import { DuplicateZipEntryError } from 'exceptions';
@@ -343,7 +342,7 @@ describe('Xpi.getFileAsStream()', function() {
         assert.equal(jsFiles[1], 'secondary.js');
 
         for (let i = 0; i < jsFiles.length; i++) {
-          assert.ok(endsWith(jsFiles[i], '.js'));
+          assert.ok(jsFiles[i].endsWith('.js'));
         }
       });
   });
@@ -364,7 +363,7 @@ describe('Xpi.getFileAsStream()', function() {
         assert.equal(cssFiles[1], 'styles.css');
 
         for (let i = 0; i < cssFiles.length; i++) {
-          assert.ok(endsWith(cssFiles[i], '.css'));
+          assert.ok(cssFiles[i].endsWith('.css'));
         }
       });
   });