--- 
+++ 
@@ -17,7 +17,7 @@
                                              final int n2)
         throws ConvergenceException, MaxCountExceededException {
 
-        final int n1n2prod = n1 * n2;
+final double n1n2prod = n1 * n2;
 
         // http://en.wikipedia.org/wiki/Mann%E2%80%93Whitney_U#Normal_approximation
         final double EU = n1n2prod / 2.0;