diff --git a/src/netif/ppp/pppos.c b/src/netif/ppp/pppos.c
index e1483042..77fde8de 100644
--- a/src/netif/ppp/pppos.c
+++ b/src/netif/ppp/pppos.c
@@ -34,6 +34,8 @@
 #include "lwip/opt.h"
 #if PPP_SUPPORT && PPPOS_SUPPORT /* don't build if not configured for use in lwipopts.h */
 
+#include <string.h>
+
 #include "lwip/err.h"
 #include "lwip/pbuf.h"
 #include "lwip/sys.h"