diff --git a/dotnet/src/dotnetframework/GxClasses/Core/GXUtilsCommon.cs b/dotnet/src/dotnetframework/GxClasses/Core/GXUtilsCommon.cs
index 985fe93d1..bc5755155 100644
--- a/dotnet/src/dotnetframework/GxClasses/Core/GXUtilsCommon.cs
+++ b/dotnet/src/dotnetframework/GxClasses/Core/GXUtilsCommon.cs
@@ -2707,6 +2707,8 @@ public string TToC(DateTime dt, int lenDate, int lenTime, int ampmFmt, int dateF
 
 		static public byte Dow(DateTime dt)
 		{
+			if (dt == nullDate)
+				return 0;
 			return (byte)(dt.DayOfWeek + 1);
 		}
 		static public string CDow(DateTime dt, string lang)