diff --git a/src/vars.c b/src/vars.c
index ad518eaf..ff008605 100644
--- a/src/vars.c
+++ b/src/vars.c
@@ -34,7 +34,7 @@
 typedef struct efi_variable_t {
 	uint16_t	VariableName[1024/sizeof(uint16_t)];
 	efi_guid_t	VendorGuid;
-	unsigned long	DataSize;
+	uint64_t	DataSize;
 	uint8_t		Data[1024];
 	efi_status_t	Status;
 	uint32_t	Attributes;