diff --git a/src/include/netif/ppp/ppp.h b/src/include/netif/ppp/ppp.h
index 09766222..6d24770f 100644
--- a/src/include/netif/ppp/ppp.h
+++ b/src/include/netif/ppp/ppp.h
@@ -303,7 +303,7 @@ struct ppp_addrs {
 /*
  * PPP interface control block.
  */
-typedef void (*link_command_cb_fn)(void *pcb, u8_t command);
+typedef int (*link_command_cb_fn)(void *pcb, u8_t command);
 typedef int (*link_write_cb_fn)(void *pcb, struct pbuf *p);
 typedef err_t (*link_netif_output_cb_fn)(void *pcb, struct pbuf *p, u_short protocol);
 
diff --git a/src/netif/ppp/pppoe.c b/src/netif/ppp/pppoe.c
index 60200e1e..ade85111 100644
--- a/src/netif/ppp/pppoe.c
+++ b/src/netif/ppp/pppoe.c
@@ -117,7 +117,7 @@ static char pppoe_error_tmp[PPPOE_ERRORSTRING_LEN];
 
 
 /* callbacks called from PPP core */
-static void pppoe_link_command_callback(void *pcb, u8_t command);
+static int pppoe_link_command_callback(void *pcb, u8_t command);
 static int pppoe_link_write_callback(void *pcb, struct pbuf *p);
 static err_t pppoe_link_netif_output_callback(void *pcb, struct pbuf *p, u_short protocol);
 
@@ -190,7 +190,7 @@ ppp_pcb *pppoe_create(struct netif *pppif,
 }
 
 /* Called by PPP core */
-static void pppoe_link_command_callback(void *pcb, u8_t command) {
+static int pppoe_link_command_callback(void *pcb, u8_t command) {
   struct pppoe_softc *sc = (struct pppoe_softc *)pcb;
 
   switch(command) {
@@ -208,6 +208,8 @@ static void pppoe_link_command_callback(void *pcb, u8_t command) {
 
   default: ;
   }
+
+  return PPPERR_NONE;
 }
 
 /* Called by PPP core */
diff --git a/src/netif/ppp/pppol2tp.c b/src/netif/ppp/pppol2tp.c
index 26af09be..04cea64b 100644
--- a/src/netif/ppp/pppol2tp.c
+++ b/src/netif/ppp/pppol2tp.c
@@ -75,7 +75,7 @@
 #endif /* PPPOL2TP_AUTH_SUPPORT */
 
 /* callbacks called from PPP core */
-static void pppol2tp_link_command_callback(void *pcb, u8_t command);
+static int pppol2tp_link_command_callback(void *pcb, u8_t command);
 static int pppol2tp_link_write_callback(void *pcb, struct pbuf *p);
 static err_t pppol2tp_link_netif_output_callback(void *pcb, struct pbuf *p, u_short protocol);
 
@@ -143,7 +143,7 @@ ppp_pcb *pppol2tp_create(struct netif *pppif,
 }
 
 /* Called by PPP core */
-static void pppol2tp_link_command_callback(void *pcb, u8_t command) {
+static int pppol2tp_link_command_callback(void *pcb, u8_t command) {
   pppol2tp_pcb *l2tp = (pppol2tp_pcb *)pcb;
 
   switch(command) {
@@ -161,6 +161,8 @@ static void pppol2tp_link_command_callback(void *pcb, u8_t command) {
 
   default: ;
   }
+
+  return PPPERR_NONE;
 }
 
 /* Called by PPP core */
diff --git a/src/netif/ppp/pppos.c b/src/netif/ppp/pppos.c
index a826f2cc..7a53b59a 100644
--- a/src/netif/ppp/pppos.c
+++ b/src/netif/ppp/pppos.c
@@ -51,7 +51,7 @@
 #include "netif/ppp/vj.h"
 
 /* callbacks called from PPP core */
-static void pppos_link_command_callback(void *pcb, u8_t command);
+static int pppos_link_command_callback(void *pcb, u8_t command);
 static int pppos_link_write_callback(void *pcb, struct pbuf *p);
 static err_t pppos_link_netif_output_callback(void *pcb, struct pbuf *pb, u_short protocol);
 
@@ -176,7 +176,7 @@ ppp_pcb *pppos_create(struct netif *pppif, sio_fd_t fd,
 }
 
 /* Called by PPP core */
-static void
+static int
 pppos_link_command_callback(void *pcb, u8_t command)
 {
   pppos_pcb *pppos = (pppos_pcb *)pcb;
@@ -196,6 +196,8 @@ pppos_link_command_callback(void *pcb, u8_t command)
 
   default: ;
   }
+
+  return PPPERR_NONE;
 }
 
 /* Called by PPP core */