diff --git a/demos/custom-fields/field_turtle.js b/demos/custom-fields/field_turtle.js
index 353ae8c1e..120a94608 100644
--- a/demos/custom-fields/field_turtle.js
+++ b/demos/custom-fields/field_turtle.js
@@ -455,11 +455,18 @@ CustomFields.FieldTurtle.prototype.updateColour = function() {
 
   var child = this.turtleGroup_.firstChild;
   while(child) {
-    // If it is a text node, or a non-turtle node.
-    if (child.nodeType == 3 || !child.classList.contains('turtleBody')) {
+    // If it is a text node, continue.
+    if (child.nodeType == 3) {
       child = child.nextSibling;
       continue;
     }
+    // Or if it is a non-turtle node, continue.
+    var className = child.getAttribute('class');
+    if (!className || className.indexOf('turtleBody') == -1) {
+      child = child.nextSibling;
+      continue;
+    }
+
     child.style.fill = fillColour;
     child.style.stroke = borderColour;
     child = child.nextSibling;
diff --git a/demos/custom-fields/index.html b/demos/custom-fields/index.html
index 7f2048669..2e1270f67 100644
--- a/demos/custom-fields/index.html
+++ b/demos/custom-fields/index.html
@@ -40,16 +40,16 @@
       <input type="button" value="Import from XML" onclick="fromXml()">
     </p>
 
-    <table style="width: 800px; height: 480px">
+    <table>
       <tr>
         <td>
           <textarea id="importExport"
-                    style="width: 200px; height: 100%;"
+                    style="width: 200px; height: 480px;"
                     onchange="textAreaChange();"
                     onkeyup="textAreaChange()"></textarea>
         </td>
         <td>
-          <div id="blocklyDiv" style="width: 600px; height: 100%;"></div>
+          <div id="blocklyDiv" style="width: 600px; height: 480px;"></div>
         </td>
       </tr>
     </table>