diff --git a/src/URI.js b/src/URI.js
index 03f2c6c1..90514f70 100644
--- a/src/URI.js
+++ b/src/URI.js
@@ -77,6 +77,10 @@
     return this;
   }
 
+  function isInteger(value) {
+    return /^[0-9]+$/.test(value);
+  }
+
   URI.version = '1.18.11';
 
   var p = URI.prototype;
@@ -1058,7 +1062,7 @@
     }
 
     var port = Number(v);
-    if (Number.isInteger(port) && (port > 0) && (port < 65536)) {
+    if (isInteger(port) && (port > 0) && (port < 65536)) {
       return;
     }
 
diff --git a/test/test.js b/test/test.js
index 8ebf8623..c19db70a 100644
--- a/test/test.js
+++ b/test/test.js
@@ -1681,6 +1681,36 @@
     deepEqual(links, expected, 'urls extracted');
     equal(result, source, 'source not modified');
   });
+  test('ensureValidPort', function() {
+
+    function testPort(value) {
+      var result = true;
+      try {
+        URI.ensureValidPort(value);
+      } catch(e) {
+        result = false;
+      }
+
+      return result;
+    }
+
+    equal(testPort(8000), true);
+    equal(testPort('8080'), true);
+
+    equal(testPort(0), true);
+    equal(testPort(1), true);
+
+    equal(testPort(65535), true);
+    equal(testPort(65536), false);
+
+    equal(testPort(-8080), false);
+    equal(testPort('-8080'), false);
+
+    equal(testPort('aaa8080'), false);
+    equal(testPort('8080a'), false);
+
+    equal(testPort(8080.2), false);
+  });
   test('noConflict', function() {
     var actual_lib = URI; // actual library; after loading, before noConflict()
     var unconflicted = URI.noConflict();