diff --git a/src/include/ipv4/lwip/ip_frag.h b/src/include/ipv4/lwip/ip_frag.h
index a982c5a6..137712e6 100644
--- a/src/include/ipv4/lwip/ip_frag.h
+++ b/src/include/ipv4/lwip/ip_frag.h
@@ -33,11 +33,17 @@
 #ifndef __LWIP_IP_FRAG_H__
 #define __LWIP_IP_FRAG_H__
 
+#include "lwip/opt.h"
 #include "lwip/err.h"
 #include "lwip/pbuf.h"
 #include "lwip/netif.h"
 #include "lwip/ip_addr.h"
 
+#ifndef IP_REASS_INTERVAL
+#define IP_REASS_INTERVAL 1000
+#endif
+
+void ip_frag_init(void);
 void ip_reass_tmr(void);
 struct pbuf * ip_reass(struct pbuf *p);
 err_t ip_frag(struct pbuf *p, struct netif *netif, struct ip_addr *dest);