diff --git a/Parsedown.php b/Parsedown.php
index c540d12..110d6e3 100644
--- a/Parsedown.php
+++ b/Parsedown.php
@@ -1554,14 +1554,7 @@ class Parsedown
             }
         }
 
-        $Element['attributes'][$attribute] = preg_replace_callback(
-            '/[^\/#?&=%]++/',
-            function (array $match)
-            {
-                return urlencode($match[0]);
-            },
-            $Element['attributes'][$attribute]
-        );
+        $Element['attributes'][$attribute] = str_replace(':', '%3A', $Element['attributes'][$attribute]);
 
         return $Element;
     }
diff --git a/test/data/xss_bad_url.html b/test/data/xss_bad_url.html
index 8e43877..0b216d1 100644
--- a/test/data/xss_bad_url.html
+++ b/test/data/xss_bad_url.html
@@ -1,16 +1,16 @@
-<p><a href="javascript%3Aalert%281%29">xss</a></p>
-<p><a href="javascript%3Aalert%281%29">xss</a></p>
-<p><a href="javascript%3A//alert%281%29">xss</a></p>
-<p><a href="javascript&amp;colon%3Balert%281%29">xss</a></p>
-<p><img src="javascript%3Aalert%281%29" alt="xss" /></p>
-<p><img src="javascript%3Aalert%281%29" alt="xss" /></p>
-<p><img src="javascript%3A//alert%281%29" alt="xss" /></p>
-<p><img src="javascript&amp;colon%3Balert%281%29" alt="xss" /></p>
-<p><a href="data%3Atext/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
-<p><a href="data%3Atext/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
-<p><a href="data%3A//text/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
-<p><a href="data&amp;colon%3Btext/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
-<p><img src="data%3Atext/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
-<p><img src="data%3Atext/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
-<p><img src="data%3A//text/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
-<p><img src="data&amp;colon%3Btext/html%3Bbase64%2CPHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
\ No newline at end of file
+<p><a href="javascript%3Aalert(1)">xss</a></p>
+<p><a href="javascript%3Aalert(1)">xss</a></p>
+<p><a href="javascript%3A//alert(1)">xss</a></p>
+<p><a href="javascript&amp;colon;alert(1)">xss</a></p>
+<p><img src="javascript%3Aalert(1)" alt="xss" /></p>
+<p><img src="javascript%3Aalert(1)" alt="xss" /></p>
+<p><img src="javascript%3A//alert(1)" alt="xss" /></p>
+<p><img src="javascript&amp;colon;alert(1)" alt="xss" /></p>
+<p><a href="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
+<p><a href="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
+<p><a href="data%3A//text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
+<p><a href="data&amp;colon;text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==">xss</a></p>
+<p><img src="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
+<p><img src="data%3Atext/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
+<p><img src="data%3A//text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
+<p><img src="data&amp;colon;text/html;base64,PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0Pg==" alt="xss" /></p>
\ No newline at end of file