diff --git a/lib/isc/include/isc/result.h b/lib/isc/include/isc/result.h
index 06c7f9f049..53200519fc 100644
--- a/lib/isc/include/isc/result.h
+++ b/lib/isc/include/isc/result.h
@@ -15,7 +15,7 @@
  * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: result.h,v 1.47 2000/08/01 01:30:40 tale Exp $ */
+/* $Id: result.h,v 1.48 2000/08/10 23:11:12 bwelling Exp $ */
 
 #ifndef ISC_RESULT_H
 #define ISC_RESULT_H 1
@@ -70,11 +70,12 @@
 #define ISC_R_NOTFILE			44	/* not a file */
 #define ISC_R_NOTDIRECTORY		45	/* not a directory */
 #define ISC_R_QUEUEFULL			46	/* queue is full */
+#define ISC_R_FAMILY			47	/* address family mismatch */
 
 /*
  * Not an result code: the number of results.
  */
-#define ISC_R_NRESULTS 			47
+#define ISC_R_NRESULTS 			48
 
 ISC_LANG_BEGINDECLS
 
diff --git a/lib/isc/result.c b/lib/isc/result.c
index a6d7c33bee..7eeb8b85a4 100644
--- a/lib/isc/result.c
+++ b/lib/isc/result.c
@@ -15,7 +15,7 @@
  * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: result.c,v 1.46 2000/08/01 01:29:43 tale Exp $ */
+/* $Id: result.c,v 1.47 2000/08/10 23:11:09 bwelling Exp $ */
 
 #include <config.h>
 
@@ -84,7 +84,8 @@ static const char *text[ISC_R_NRESULTS] = {
 	"invalid use of multicast address",	/* 43 */
 	"not a file",				/* 44 */
 	"not a directory",			/* 45 */
-	"queue is full"				/* 46 */
+	"queue is full",			/* 46 */
+	"address family mismatch"		/* 47 */
 };
 
 #define ISC_RESULT_RESULTSET			2
diff --git a/lib/isc/unix/socket.c b/lib/isc/unix/socket.c
index fd5e34a40c..c82b1550d2 100644
--- a/lib/isc/unix/socket.c
+++ b/lib/isc/unix/socket.c
@@ -15,7 +15,7 @@
  * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: socket.c,v 1.155 2000/08/10 21:47:46 bwelling Exp $ */
+/* $Id: socket.c,v 1.156 2000/08/10 23:11:11 bwelling Exp $ */
 
 #include <config.h>
 
@@ -134,6 +134,7 @@ struct isc_socket {
 	ISC_LINK(isc_socket_t)	link;
 	unsigned int		references;
 	int			fd;
+	int			pf;
 	isc_result_t		recv_result;
 	isc_result_t		send_result;
 
@@ -1149,6 +1150,7 @@ isc_socket_create(isc_socketmgr_t *manager, int pf, isc_sockettype_t type,
 	if (ret != ISC_R_SUCCESS)
 		return (ret);
 
+	sock->pf = pf;
 	switch (type) {
 	case isc_sockettype_udp:
 		sock->fd = socket(pf, SOCK_DGRAM, IPPROTO_UDP);
@@ -2575,6 +2577,10 @@ isc_socket_bind(isc_socket_t *sock, isc_sockaddr_t *sockaddr) {
 
 	INSIST(!sock->bound);
 
+	if (sock->pf != sockaddr->type.sa.sa_family) {
+		UNLOCK(&sock->lock);
+		return(ISC_R_FAMILY);
+	}
 	if (setsockopt(sock->fd, SOL_SOCKET, SO_REUSEADDR, (void *)&on,
 		       sizeof on) < 0) {
 		UNEXPECTED_ERROR(__FILE__, __LINE__, "setsockopt(%d) failed",