diff --git a/lib/discrepances.js b/lib/discrepances.js
index 42bec64..399589b 100644
--- a/lib/discrepances.js
+++ b/lib/discrepances.js
@@ -26,12 +26,17 @@
 var discrepances = {};
 /*jshint +W004 */
 
+function getType(variable) {
+    if(null === variable) { return 'null'; }
+    return typeof variable;
+}
+
 discrepances = function discrepances(a, b){
     if(a === b){
         return null;
     }
-    var typeA = typeof a;
-    var typeB = typeof b;
+    var typeA = getType(a);
+    var typeB = getType(b);
     if(typeA === typeB) {
         if(typeA === 'number') {
             return {difference:a-b, values:[a,b]};
diff --git a/test/test.js b/test/test.js
index 7d5b876..71d5bff 100644
--- a/test/test.js
+++ b/test/test.js
@@ -9,7 +9,7 @@ describe("discrepances", function(){
         {a:4                 , b:4                  , expected: null                                                                      },
         {a:4                 , b:5                  , expected: {difference:-1             , values:[4, 5]                               }},
         {a:"4"               , b:4                  , expected: {types:['string', 'number'], values:["4", 4]                             }},
-        {skip:true, a:null              , b:0                  , expected: {types:['null'  , 'number'], values:[null, 0]                            }},
+        {a:null              , b:0                  , expected: {types:['null'  , 'number'], values:[null, 0]                            }},
         {skip:true, a:new Date()        , b:/a/                , expected: {class:['Date'  , 'RegExp'], values:[new Date(), /a/]                    }},
         {skip:true, a:new Date(2011,1,3), b:new Date(2011,1,4) , expected: {difference:'a definir', values:[new Date(2011,1,3), new Date(2011,1,4)] }},
         {skip:true, a:[1,2,3,4,5]       , b:[1,2,33,4,5,6]     , expected: {array:{length:discrepances(5,6), 2:discrepances(3,33)}                  }},