diff --git a/src/netif/ppp/ipcp.c b/src/netif/ppp/ipcp.c
index 3da1ba67..d5b25188 100644
--- a/src/netif/ppp/ipcp.c
+++ b/src/netif/ppp/ipcp.c
@@ -49,6 +49,8 @@
  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+#include <string.h>
+
 #include "ppp.h"
 #if PPP_SUPPORT > 0
 #include "auth.h"
diff --git a/src/netif/ppp/lcp.c b/src/netif/ppp/lcp.c
index fb084a86..e974a2d4 100644
--- a/src/netif/ppp/lcp.c
+++ b/src/netif/ppp/lcp.c
@@ -49,6 +49,9 @@
  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  */
+ 
+#include <string.h>
+ 
 #include "ppp.h"
 #if PPP_SUPPORT > 0
 #include "fsm.h"
diff --git a/src/netif/ppp/ppp.c b/src/netif/ppp/ppp.c
index 8f3aa6ee..098f2d98 100644
--- a/src/netif/ppp/ppp.c
+++ b/src/netif/ppp/ppp.c
@@ -78,6 +78,9 @@
  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  */
+ 
+#include <string.h>
+ 
 #include "ppp.h"
 #if PPP_SUPPORT > 0
 #include "randm.h"
diff --git a/src/netif/ppp/vj.c b/src/netif/ppp/vj.c
index 7615bb5b..0636ee11 100644
--- a/src/netif/ppp/vj.c
+++ b/src/netif/ppp/vj.c
@@ -28,11 +28,12 @@
  * for a 16 bit processor.
  */
 
+#include <string.h>
+
 #include "ppp.h"
 #include "vj.h"
 #include "pppdebug.h"
 
-
 #if VJ_SUPPORT > 0
 
 #if LINK_STATS