diff --git a/src/BossFrog.cpp b/src/BossFrog.cpp
index 24f1f41e..2a8dc8e4 100644
--- a/src/BossFrog.cpp
+++ b/src/BossFrog.cpp
@@ -1,5 +1,7 @@
 #include "BossFrog.h"
 
+#include <stddef.h>
+
 #include "WindowsWrapper.h"
 
 #include "Boss.h"
diff --git a/src/BossIronH.cpp b/src/BossIronH.cpp
index e1cc4998..d845a9db 100644
--- a/src/BossIronH.cpp
+++ b/src/BossIronH.cpp
@@ -1,5 +1,7 @@
 #include "BossIronH.h"
 
+#include <stddef.h>
+
 #include "WindowsWrapper.h"
 
 #include "Boss.h"
diff --git a/src/BossPress.cpp b/src/BossPress.cpp
index 63edd596..1636d009 100644
--- a/src/BossPress.cpp
+++ b/src/BossPress.cpp
@@ -1,5 +1,7 @@
 #include "BossPress.h"
 
+#include <stddef.h>
+
 #include "WindowsWrapper.h"
 
 #include "Boss.h"
diff --git a/src/BossTwinD.cpp b/src/BossTwinD.cpp
index 5e9cac15..849093d0 100644
--- a/src/BossTwinD.cpp
+++ b/src/BossTwinD.cpp
@@ -1,5 +1,7 @@
 #include "BossTwinD.h"
 
+#include <stddef.h>
+
 #include "WindowsWrapper.h"
 
 #include "Boss.h"
diff --git a/src/BulHit.cpp b/src/BulHit.cpp
index 065d8659..e9524af0 100644
--- a/src/BulHit.cpp
+++ b/src/BulHit.cpp
@@ -1,5 +1,7 @@
 #include "BulHit.h"
 
+#include <stddef.h>
+
 #include "Bullet.h"
 #include "Caret.h"
 #include "Game.h"
diff --git a/src/Bullet.cpp b/src/Bullet.cpp
index c7157f85..c6d3fb4d 100644
--- a/src/Bullet.cpp
+++ b/src/Bullet.cpp
@@ -1,5 +1,6 @@
 #include "Bullet.h"
 
+#include <stddef.h>
 #include <string.h>
 
 #include "WindowsWrapper.h"
diff --git a/src/Ending.cpp b/src/Ending.cpp
index 0d3dfe7e..ac7cec78 100644
--- a/src/Ending.cpp
+++ b/src/Ending.cpp
@@ -1,5 +1,6 @@
 #include "Ending.h"
 
+#include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
diff --git a/src/MyChar.cpp b/src/MyChar.cpp
index 035f9407..b477006f 100644
--- a/src/MyChar.cpp
+++ b/src/MyChar.cpp
@@ -1,5 +1,6 @@
 #include "MyChar.h"
 
+#include <stddef.h>
 #include <string.h>
 
 #include "WindowsWrapper.h"
diff --git a/src/MycParam.cpp b/src/MycParam.cpp
index fbc032b3..76f8f55a 100644
--- a/src/MycParam.cpp
+++ b/src/MycParam.cpp
@@ -1,5 +1,6 @@
 #include "MycParam.h"
 
+#include <stddef.h>
 #include <stdio.h>
 
 #include "WindowsWrapper.h"
diff --git a/src/NpcAct120.cpp b/src/NpcAct120.cpp
index 68e37bf5..df019784 100644
--- a/src/NpcAct120.cpp
+++ b/src/NpcAct120.cpp
@@ -1,5 +1,6 @@
 #include "NpcAct.h"
 
+#include <stddef.h>
 #include <stdio.h>
 
 #include "WindowsWrapper.h"
diff --git a/src/NpcAct240.cpp b/src/NpcAct240.cpp
index 902f1d8d..3d3120f4 100644
--- a/src/NpcAct240.cpp
+++ b/src/NpcAct240.cpp
@@ -1,5 +1,7 @@
 #include "NpcAct.h"
 
+#include <stddef.h>
+
 #include "WindowsWrapper.h"
 
 #include "Caret.h"
diff --git a/src/TextScr.cpp b/src/TextScr.cpp
index 0a434fe8..d7d6fe00 100644
--- a/src/TextScr.cpp
+++ b/src/TextScr.cpp
@@ -1,5 +1,6 @@
 #include "TextScr.h"
 
+#include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>