diff --git a/src/core/netif.c b/src/core/netif.c
index 549a3972..31396e1a 100644
--- a/src/core/netif.c
+++ b/src/core/netif.c
@@ -55,7 +55,7 @@ struct netif *
 netif_add(struct ip_addr *ipaddr, struct ip_addr *netmask,
 	  struct ip_addr *gw,
 	  void *state,
-	  void (* init)(struct netif *netif),
+	  err_t (* init)(struct netif *netif),
 	  err_t (* input)(struct pbuf *p, struct netif *netif))
 {
   struct netif *netif;
@@ -74,8 +74,11 @@ netif_add(struct ip_addr *ipaddr, struct ip_addr *netmask,
   ip_addr_set(&(netif->netmask), netmask);
   ip_addr_set(&(netif->gw), gw);
 
-  init(netif);
-  
+  if (init(netif) != ERR_OK) {
+      mem_free(netif);
+      return NULL;
+  }
+ 
   netif->next = netif_list;
   netif_list = netif;
 #if NETIF_DEBUG
diff --git a/src/include/lwip/err.h b/src/include/lwip/err.h
index c7a52e2b..baab539d 100644
--- a/src/include/lwip/err.h
+++ b/src/include/lwip/err.h
@@ -58,6 +58,7 @@ typedef s8_t err_t;
 
 #define ERR_USE  -10     /* Address in use.          */
 
+#define ERR_IF   -11     /* Low-level netif error    */
 
 
 #ifdef LWIP_DEBUG
diff --git a/src/include/lwip/netif.h b/src/include/lwip/netif.h
index 9fbc4826..e92ead72 100644
--- a/src/include/lwip/netif.h
+++ b/src/include/lwip/netif.h
@@ -114,7 +114,7 @@ void netif_init(void);
 struct netif *netif_add(struct ip_addr *ipaddr, struct ip_addr *netmask,
 			struct ip_addr *gw,
 			void *state,
-			void (* init)(struct netif *netif),
+			err_t (* init)(struct netif *netif),
 			err_t (* input)(struct pbuf *p, struct netif *netif));
 
 void netif_remove(struct netif * netif);
diff --git a/src/include/netif/loopif.h b/src/include/netif/loopif.h
index cdd6dd23..086f8121 100644
--- a/src/include/netif/loopif.h
+++ b/src/include/netif/loopif.h
@@ -34,6 +34,6 @@
 
 #include "lwip/netif.h"
 
-void loopif_init(struct netif *netif);
+err_t loopif_init(struct netif *netif);
 
 #endif /* __NETIF_LOOPIF_H__ */
diff --git a/src/include/netif/slipif.h b/src/include/netif/slipif.h
index af9393f0..bf70046a 100644
--- a/src/include/netif/slipif.h
+++ b/src/include/netif/slipif.h
@@ -36,7 +36,7 @@
 
 #include "lwip/netif.h"
 
-void slipif_init(struct netif * netif);
+err_t slipif_init(struct netif * netif);
  
 #endif 
 
diff --git a/src/netif/loopif.c b/src/netif/loopif.c
index 40b85edf..bdfef854 100644
--- a/src/netif/loopif.c
+++ b/src/netif/loopif.c
@@ -67,12 +67,13 @@ loopif_output(struct netif *netif, struct pbuf *p,
   return ERR_MEM;
 }
 /*-----------------------------------------------------------------------------------*/
-void
+err_t
 loopif_init(struct netif *netif)
 {
   netif->name[0] = 'l';
   netif->name[1] = 'o';
   netif->output = loopif_output;
+  return ERR_OK;
 }
 /*-----------------------------------------------------------------------------------*/
 
diff --git a/src/netif/slipif.c b/src/netif/slipif.c
index 7f360f51..49136f1b 100644
--- a/src/netif/slipif.c
+++ b/src/netif/slipif.c
@@ -197,7 +197,7 @@ slipif_loop(void *nf)
  * Call the arch specific sio_open and remember
  * the opened device in the state field of the netif.
  */ 
-void
+err_t
 slipif_init(struct netif *netif)
 {
 	
@@ -209,6 +209,9 @@ slipif_init(struct netif *netif)
   netif->mtu = 1500;	
 
   netif->state = sio_open(netif->num);
+  if (!netif->state)
+      return ERR_IF;
 
   sys_thread_new(slipif_loop, netif);
+  return ERR_OK;
 }