diff --git a/src/markup/render.php b/src/markup/render.php
index 0105ce2..f56bc70 100644
--- a/src/markup/render.php
+++ b/src/markup/render.php
@@ -1,42 +1,45 @@
 <?php
 
 /*
  * Copyright 2011 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *   http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 /**
  * @group markup
  */
 function phutil_render_tag($tag, array $attributes = array(), $content = null) {
   foreach ($attributes as $k => $v) {
+    if ($v === null) {
+      continue;
+    }
     $v = phutil_escape_html($v);
     $attributes[$k] = ' '.$k.'="'.$v.'"';
   }
 
   $attributes = implode('', $attributes);
 
   if ($content === null) {
     return '<'.$tag.$attributes.' />';
   } else {
     return '<'.$tag.$attributes.'>'.$content.'</'.$tag.'>';
   }
 }
 
 /**
  * @group markup
  */
 function phutil_escape_html($string) {
   return htmlspecialchars($string, ENT_QUOTES, 'UTF-8');
 }