diff --git a/htroot/yacy/crawlOrder.java b/htroot/yacy/crawlOrder.java
index 9af1f6a97..e17de4754 100644
--- a/htroot/yacy/crawlOrder.java
+++ b/htroot/yacy/crawlOrder.java
@@ -177,7 +177,7 @@ public final class crawlOrder {
                     if (!newURL.equals(urlv.get(0))) {
                         env.getLog().logWarning("crawlOrder: Received not normalized URL " + urlv.get(0));    
                     }
-                    String refURL = new URL((String) refv.get(0)).toNormalform();
+                    String refURL = (refv.get(0) == null) ? null : new URL((String) refv.get(0)).toNormalform();
                     if ((refURL != null) && (!refURL.equals(refv.get(0)))) {
                         env.getLog().logWarning("crawlOrder: Received not normalized Referer URL " + refv.get(0) + " of URL " + urlv.get(0));    
                     }
diff --git a/source/de/anomic/net/URL.java b/source/de/anomic/net/URL.java
index 3c06cc96f..48475e503 100644
--- a/source/de/anomic/net/URL.java
+++ b/source/de/anomic/net/URL.java
@@ -38,6 +38,7 @@ public class URL {
     private int port;
     
     public URL(String url) throws MalformedURLException {
+        if (url == null) throw new MalformedURLException("url string is null");
         parseURLString(url);
     }