diff --git a/src/netif/etharp.c b/src/netif/etharp.c
index 093ad97f..dec48b52 100644
--- a/src/netif/etharp.c
+++ b/src/netif/etharp.c
@@ -55,6 +55,11 @@
 #include "lwip/dhcp.h"
 #include "lwip/autoip.h"
 #include "netif/etharp.h"
+
+#if PPPOE_SUPPORT
+#include "netif/ppp_oe.h"
+#endif /* PPPOE_SUPPORT */
+
 #include <string.h>
 
 /** the time an ARP entry stays valid after its last update,
diff --git a/src/netif/ppp/lcp.c b/src/netif/ppp/lcp.c
index 57b0a3d9..85b92c6b 100644
--- a/src/netif/ppp/lcp.c
+++ b/src/netif/ppp/lcp.c
@@ -67,7 +67,7 @@
 #include <string.h>
 
 #if PPPOE_SUPPORT
-#include "ppp_oe.h"
+#include "netif/ppp_oe.h"
 #else
 #define PPPOE_MAXMTU PPP_MAXMRU
 #endif
diff --git a/src/netif/ppp/ppp.c b/src/netif/ppp/ppp.c
index 7ec0a2df..a0cd7308 100644
--- a/src/netif/ppp/ppp.c
+++ b/src/netif/ppp/ppp.c
@@ -102,7 +102,7 @@
 #include "vj.h"
 #endif /* VJ_SUPPORT */
 #if PPPOE_SUPPORT
-#include "ppp_oe.h"
+#include "netif/ppp_oe.h"
 #endif /* PPPOE_SUPPORT */
 
 #include <string.h>
diff --git a/src/netif/ppp/ppp_oe.c b/src/netif/ppp/ppp_oe.c
index e62969ff..1e8ee948 100644
--- a/src/netif/ppp/ppp_oe.c
+++ b/src/netif/ppp/ppp_oe.c
@@ -73,12 +73,13 @@
 #if PPPOE_SUPPORT /* don't build if not configured for use in lwipopts.h */
 
 #include "ppp.h"
-#include "ppp_oe.h"
 #include "pppdebug.h"
 
-#include "netif/etharp.h"
 #include "lwip/sys.h"
 
+#include "netif/ppp_oe.h"
+#include "netif/etharp.h"
+
 #include "queue.h"
 
 #include <string.h>
diff --git a/src/netif/slipif.c b/src/netif/slipif.c
index d7604126..b3788593 100644
--- a/src/netif/slipif.c
+++ b/src/netif/slipif.c
@@ -51,10 +51,10 @@
 #include "lwip/snmp.h"
 #include "lwip/sio.h"
 
-#define SLIP_END     0300
-#define SLIP_ESC     0333
-#define SLIP_ESC_END 0334
-#define SLIP_ESC_ESC 0335
+#define SLIP_END     0300 /* 0xC0 */
+#define SLIP_ESC     0333 /* 0xDB */
+#define SLIP_ESC_END 0334 /* 0xDC */
+#define SLIP_ESC_ESC 0335 /* 0xDD */
 
 #define MAX_SIZE     1500
 
@@ -180,6 +180,7 @@ slipif_input(struct netif *netif)
           q = p;
         }
       }
+
       /* this automatically drops bytes if > MAX_SIZE */
       if ((p != NULL) && (recved <= MAX_SIZE)) {
         ((u8_t *)p->payload)[i] = c;
@@ -192,7 +193,7 @@ slipif_input(struct netif *netif)
             /* p is a chain, on to the next in the chain */
             p = p->next;
           } else {
-            /* p is a signle pbuf, set it to NULL so next time a new
+            /* p is a single pbuf, set it to NULL so next time a new
              * pbuf is allocated */
             p = NULL;
           }