diff --git a/stand/efi/loader/copy.c b/stand/efi/loader/copy.c
index 3f2d1c6c20b0..a0aea9823632 100644
--- a/stand/efi/loader/copy.c
+++ b/stand/efi/loader/copy.c
@@ -36,7 +36,7 @@
 #include "loader_efi.h"
 
 #define	M(x)	((x) * 1024 * 1024)
-#define	G(x)	(1UL * (x) * 1024 * 1024 * 1024)
+#define	G(x)	(1ULL * (x) * 1024 * 1024 * 1024)
 
 #if defined(__amd64__)
 #include <machine/cpufunc.h>