diff --git a/ChangeLog b/ChangeLog
index 00c154ed7..5be787e99 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2013-11-07  Vladimir Serbinenko  <phcoder@gmail.com>
+
+	* grub-core/net/bootp.c (OFFSET_OF): Explicitly cast to grub_size_t.
+
 2013-11-07  Vladimir Serbinenko  <phcoder@gmail.com>
 
 	* grub-core/net/bootp.c (set_env_limn_ro): Make pointer const.
diff --git a/grub-core/net/bootp.c b/grub-core/net/bootp.c
index 76fee9183..ed159418a 100644
--- a/grub-core/net/bootp.c
+++ b/grub-core/net/bootp.c
@@ -159,7 +159,7 @@ parse_dhcp_vendor (const char *name, const void *vend, int limit, int *mask)
     }
 }
 
-#define OFFSET_OF(x, y) ((grub_uint8_t *)((y)->x) - (grub_uint8_t *)(y))
+#define OFFSET_OF(x, y) ((grub_size_t)((grub_uint8_t *)((y)->x) - (grub_uint8_t *)(y)))
 
 struct grub_net_network_level_interface *
 grub_net_configure_by_dhcp_ack (const char *name,