diff --git a/service/ptos/head/hal/mmio.h b/service/ptos/head/hal/mmio.h
index 67b3e4d..f02fa56 100644
--- a/service/ptos/head/hal/mmio.h
+++ b/service/ptos/head/hal/mmio.h
@@ -9,7 +9,7 @@
 #ifndef _MU_MMIO_H_
 #define _MU_MMIO_H_ 1
 
-#include <stdef.h>
+#include <ptdef.h>
 
 /* Builds mmio_write<n> functions */
 #define _MMIO_WRITE_BUILDER(NAME, TYPE)         \