diff --git a/src/include/netif/ppp/ppp_impl.h b/src/include/netif/ppp/ppp_impl.h
index 8b82f314..0c34c90e 100644
--- a/src/include/netif/ppp/ppp_impl.h
+++ b/src/include/netif/ppp/ppp_impl.h
@@ -39,6 +39,7 @@
 
 #include <stdio.h> /* formats */
 #include <stdarg.h>
+#include <string.h>
 
 #include "lwip/netif.h"
 #include "lwip/def.h"