diff --git a/src/netif/ppp/pppos.c b/src/netif/ppp/pppos.c
index eaeb2d12..54164298 100644
--- a/src/netif/ppp/pppos.c
+++ b/src/netif/ppp/pppos.c
@@ -35,8 +35,8 @@
 #if PPP_SUPPORT && PPPOS_SUPPORT /* don't build if not configured for use in lwipopts.h */
 
 #include <string.h>
-#include <stddef.h>
 
+#include "lwip/arch.h"
 #include "lwip/err.h"
 #include "lwip/pbuf.h"
 #include "lwip/sys.h"