diff --git a/SmartSQL/SmartSQL.Framework/Util/MapHelper/SqlServerDbTypeMapHelper.cs b/SmartSQL/SmartSQL.Framework/Util/MapHelper/SqlServerDbTypeMapHelper.cs
index 0243c4b3c6fecf0ed3da47520497f71249378bf9..7c0fa46d60c3747abdec7972911692c88358f448 100644
--- a/SmartSQL/SmartSQL.Framework/Util/MapHelper/SqlServerDbTypeMapHelper.cs
+++ b/SmartSQL/SmartSQL.Framework/Util/MapHelper/SqlServerDbTypeMapHelper.cs
@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
@@ -15,7 +15,7 @@ namespace SmartSQL.Framework.Util
             string csharpType = "object";
             switch (dbtype)
             {
-                case "bigint": csharpType = "long"; break;
+                case "bigint": csharpType = isNullable ? "long?" : "long"; break;
                 case "binary": csharpType = "byte[]"; break;
                 case "bit": csharpType = isNullable ? "bool?" : "bool"; break;
                 case "char": csharpType = "string"; break;