diff --git a/htroot/CrawlStartExpert_p.html b/htroot/CrawlStartExpert_p.html
index a8e87e5b7..60e0fa073 100644
--- a/htroot/CrawlStartExpert_p.html
+++ b/htroot/CrawlStartExpert_p.html
@@ -73,7 +73,7 @@
           <td><label for="crawlingFilter">Crawling Filter</label>:</td>
           <td>
 			<input name="crawlingFilter" id="crawlingFilter" type="text" size="20" maxlength="100" value="#[crawlingFilter]#" />
-			<input type="button" value="only one domain" onclick='var domain=prompt("please enter domain without \"www.\" (i.e. \"yacy.net\").");document.getElementById("crawlingFilter").value=".*\\."+domain.replace("\.", "\\.")+"/.*"' />
+			<input type="button" value="only one domain" onclick='var domain=prompt("please enter domain without \"www.\" (i.e. \"yacy.net\").");if(domain!=null){document.getElementById("crawlingFilter").value=".*\\."+domain.replace("\.", "\\.")+"/.*"}' />
 		  </td>
           <td>
             This is an emacs-like regular expression that must match with the URLs which are used to be crawled.