diff --git a/cdblock.h b/cdblock.h
index f16a69c..de72e6a 100644
--- a/cdblock.h
+++ b/cdblock.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "type.h"
 
 struct cr_rr {
diff --git a/scsp.h b/scsp.h
index 9f7f182..6c16941 100644
--- a/scsp.h
+++ b/scsp.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "type.h"
 
 // Because the main CPU cannot access in units of 8 bits, so read and write in
diff --git a/scu.h b/scu.h
index e426ccc..d88d292 100644
--- a/scu.h
+++ b/scu.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "type.h"
 
 typedef struct scu_reg {
diff --git a/sh2.h b/sh2.h
index 2c9cb15..4560ff8 100644
--- a/sh2.h
+++ b/sh2.h
@@ -2,8 +2,6 @@
 
 #include "type.h"
 
-#include <cstddef>
-
 typedef struct sh2_reg {
   reg8 SMR;      // 0x000
   reg8 BRR;      // 0x001
diff --git a/smpc.h b/smpc.h
index 39c6105..35cc9b6 100644
--- a/smpc.h
+++ b/smpc.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "type.h"
 
 struct ioreg {
diff --git a/type.h b/type.h
index 629de0f..1f77a91 100644
--- a/type.h
+++ b/type.h
@@ -1,8 +1,8 @@
+#include <stddef.h>
 #include <stdint.h>
 
 #ifndef __cplusplus
 #define static_assert _Static_assert
-#define offsetof __builtin_offsetof
 #endif
 
 typedef volatile uint8_t reg8;
diff --git a/vdp1.h b/vdp1.h
index ae5f8a8..664cd38 100644
--- a/vdp1.h
+++ b/vdp1.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "type.h"
 
 /* command table */
diff --git a/vdp2.h b/vdp2.h
index c761ba9..451407d 100644
--- a/vdp2.h
+++ b/vdp2.h
@@ -1,3 +1,5 @@
+#pragma once
+
 #include "type.h"
 
 /* memory offsets */