SharePoint 2013: custom masterpage elements showing up in dialog box

I tried to include a custom header in a standard SharePoint 2013 masterpage (“Seattle”), unfortunately, the new content header was showing up in every dialog box too. I found a quick and easy work-around to prevent the custom code from being rendered. Just wrap the whole custom code in a div tag and add a class called “s4-notdlg” to that div – works like a charm!

<div class="s4-notdlg">   
..custom code...  
</div>