diff --git a/ospfd/ospf_packet.c b/ospfd/ospf_packet.c
index 8b818d7..d41fff5 100644
--- a/ospfd/ospf_packet.c
+++ b/ospfd/ospf_packet.c
@@ -32,6 +32,7 @@
 #include "stream.h"
 #include "log.h"
 #include "sockopt.h"
+#include "checksum.h"
 #include "md5.h"
 
 #include "ospfd/ospfd.h"
@@ -59,8 +60,6 @@
   "Link State Acknowledgment",
 };
 
-extern int in_cksum (void *ptr, int nbytes);
-
 /* OSPF authentication checking function */
 static int
 ospf_auth_type (struct ospf_interface *oi)
@@ -2193,7 +2192,6 @@
 {
   u_int32_t ret;
   u_int16_t sum;
-  int in_cksum (void *ptr, int nbytes);
 
   /* clear auth_data for checksum. */
   memset (ospfh->u.auth_data, 0, OSPF_AUTH_SIMPLE_SIZE);