Index: src/java/org/apache/nutch/crawl/PartitionUrlByHost.java
===================================================================
--- src/java/org/apache/nutch/crawl/PartitionUrlByHost.java	(revision 439953)
+++ src/java/org/apache/nutch/crawl/PartitionUrlByHost.java	(working copy)
@@ -37,6 +37,9 @@
                           int numReduceTasks) {
     String urlString = ((UTF8)key).toString();
     URL url = null;
+    if (numReduceTasks < 1) {
+    	numReduceTasks = 1;
+    }
     try {
       url = new URL(urlString);
     } catch (MalformedURLException e) {