diff --git a/proto/rip/rip.c b/proto/rip/rip.c
index 698f0e28..643fc432 100644
--- a/proto/rip/rip.c
+++ b/proto/rip/rip.c
@@ -53,6 +53,7 @@
 #include "lib/string.h"
 
 #include "rip.h"
+#include <assert.h>
 
 #define P ((struct rip_proto *) p)
 #define P_CF ((struct rip_proto_config *)p->cf)
@@ -538,6 +539,11 @@ rip_start(struct proto *p)
   struct rip_interface *rif;
   DBG( "RIP: starting instance...\n" );
 
+  assert( sizeof(struct rip_packet_heading) == 4);
+  assert( sizeof(struct rip_block) == 20);
+  assert( sizeof(struct rip_block_auth) == 20);
+
+
   P->magic = RIP_MAGIC;
   fib_init( &P->rtable, p->pool, sizeof( struct rip_entry ), 0, NULL );
   init_list( &P->connections );
diff --git a/proto/rip/rip.h b/proto/rip/rip.h
index 67fd5b0a..30002ea3 100644
--- a/proto/rip/rip.h
+++ b/proto/rip/rip.h
@@ -52,7 +52,7 @@ struct rip_block {	/* 20 bytes */
   u32 metric;
 };
 #else
-struct rip_block { /* IPv6 version! */
+struct rip_block { /* IPv6 version!, 20 bytes, too */
   ip_addr network;
   u16 tag;
   u8 pxlen;