diff --git a/src/include/netif/ppp/fsm.h b/src/include/netif/ppp/fsm.h
index dbffd93c..139ff7fb 100644
--- a/src/include/netif/ppp/fsm.h
+++ b/src/include/netif/ppp/fsm.h
@@ -73,7 +73,7 @@
  */
 typedef struct fsm {
     ppp_pcb *pcb;		/* PPP Interface */
-    struct fsm_callbacks *callbacks;	/* Callback routines */
+    const struct fsm_callbacks *callbacks;	/* Callback routines */
     char *term_reason;		/* Reason for closing protocol */
     u8_t seen_ack;		/* Have received valid Ack/Nak/Rej to Req */
 				  /* -- This is our only flag, we might use u_int :1 if we have more flags */
diff --git a/src/netif/ppp/ccp.c b/src/netif/ppp/ccp.c
index a5785329..860374bc 100644
--- a/src/netif/ppp/ccp.c
+++ b/src/netif/ppp/ccp.c
@@ -230,7 +230,7 @@ static int  ccp_extcode (fsm *, int, int, u_char *, int);
 static void ccp_rack_timeout (void *);
 static char *method_name (ccp_options *, ccp_options *);
 
-static fsm_callbacks ccp_callbacks = {
+static const fsm_callbacks ccp_callbacks = {
     ccp_resetci,
     ccp_cilen,
     ccp_addci,
diff --git a/src/netif/ppp/ecp.c b/src/netif/ppp/ecp.c
index dc7e3127..728fb5fb 100644
--- a/src/netif/ppp/ecp.c
+++ b/src/netif/ppp/ecp.c
@@ -133,7 +133,7 @@ ecp_options ecp_gotoptions[NUM_PPP];	/* what the peer agreed to do */
 ecp_options ecp_allowoptions[NUM_PPP];	/* what we'll agree to do */
 ecp_options ecp_hisoptions[NUM_PPP];	/* what we agreed to do */
 
-static fsm_callbacks ecp_callbacks = {
+static const fsm_callbacks ecp_callbacks = {
     NULL, /* ecp_resetci, */
     NULL, /* ecp_cilen, */
     NULL, /* ecp_addci, */
diff --git a/src/netif/ppp/ipcp.c b/src/netif/ppp/ipcp.c
index efb56a12..efe5d708 100644
--- a/src/netif/ppp/ipcp.c
+++ b/src/netif/ppp/ipcp.c
@@ -121,7 +121,7 @@ static void ipcp_up(fsm *f);		/* We're UP */
 static void ipcp_down(fsm *f);		/* We're DOWN */
 static void ipcp_finished(fsm *f);	/* Don't need lower layer */
 
-static fsm_callbacks ipcp_callbacks = { /* IPCP callback routines */
+static const fsm_callbacks ipcp_callbacks = { /* IPCP callback routines */
     ipcp_resetci,		/* Reset our Configuration Information */
     ipcp_cilen,			/* Length of our Configuration Information */
     ipcp_addci,			/* Add our Configuration Information */
diff --git a/src/netif/ppp/ipv6cp.c b/src/netif/ppp/ipv6cp.c
index 96142ce0..8fb01ada 100644
--- a/src/netif/ppp/ipv6cp.c
+++ b/src/netif/ppp/ipv6cp.c
@@ -188,7 +188,7 @@ static void ipv6cp_up(fsm *f); /* We're UP */
 static void ipv6cp_down(fsm *f); /* We're DOWN */
 static void ipv6cp_finished(fsm *f); /* Don't need lower layer */
 
-static fsm_callbacks ipv6cp_callbacks = { /* IPV6CP callback routines */
+static const fsm_callbacks ipv6cp_callbacks = { /* IPV6CP callback routines */
     ipv6cp_resetci,		/* Reset our Configuration Information */
     ipv6cp_cilen,		/* Length of our Configuration Information */
     ipv6cp_addci,		/* Add our Configuration Information */
diff --git a/src/netif/ppp/lcp.c b/src/netif/ppp/lcp.c
index 03783b05..76cec49e 100644
--- a/src/netif/ppp/lcp.c
+++ b/src/netif/ppp/lcp.c
@@ -241,7 +241,7 @@ static void LcpSendEchoRequest(fsm *f);
 static void LcpLinkFailure(fsm *f);
 static void LcpEchoCheck(fsm *f);
 
-static fsm_callbacks lcp_callbacks = {	/* LCP callback routines */
+static const fsm_callbacks lcp_callbacks = {	/* LCP callback routines */
     lcp_resetci,		/* Reset our Configuration Information */
     lcp_cilen,			/* Length of our Configuration Information */
     lcp_addci,			/* Add our Configuration Information */
diff --git a/src/netif/ppp/pppoe.c b/src/netif/ppp/pppoe.c
index 65dd39df..bf69c680 100644
--- a/src/netif/ppp/pppoe.c
+++ b/src/netif/ppp/pppoe.c
@@ -106,6 +106,7 @@
 #define IFF_PASSIVE IFF_LINK0 /* wait passively for connection */
 #endif
 
+/* FIXME: we should probably remove that, this is only used for debug purposes */
 #ifndef PPPOE_ERRORSTRING_LEN
 #define PPPOE_ERRORSTRING_LEN     64
 #endif