diff --git a/sources/GRIDVEL.h b/sources/GRIDVEL.h
index 8cddcd4..08aca9b 100644
--- a/sources/GRIDVEL.h
+++ b/sources/GRIDVEL.h
@@ -1,3 +1,4 @@
+#pragma once
 #include "DataAdapters/gridfile.h"
 #include "mdatetime.h"
 #include "simple2ddata.h"