Index: tests/sys/netinet/fibs_test.sh
===================================================================
--- tests/sys/netinet/fibs_test.sh
+++ tests/sys/netinet/fibs_test.sh
@@ -798,6 +798,92 @@
 	cleanup_ifaces
 }
 
+# Test that a route can be modified with "route change $SUBNET/$MASK" without
+# needing to also specify the gateway of the route.
+atf_test_case ipv4_change_route_without_dest cleanup
+ipv4_change_route_without_dest_head()
+{
+	atf_set "descr" "Test modifying a route without re-specifying its gateway"
+	atf_set "require.user" "root"
+	atf_set "require.config" "fibs"
+}
+
+ipv4_change_route_without_dest_body()
+{
+	# Configure the TAP interfaces to use a RFC5737 nonrouteable addresses
+	# and a non-default fib
+	SUBNET_PREFIX="192.0.2"
+	SUBNET="${SUBNET_PREFIX}.0"
+	ADDR0="${SUBNET_PREFIX}.1"
+	ADDR1="${SUBNET_PREFIX}.2"
+
+	MASK="24"
+
+	# Check system configuration
+	if [ 0 != `sysctl -n net.add_addr_allfibs` ]; then
+		atf_skip "This test requires net.add_addr_allfibs=0"
+	fi
+	get_fibs 1
+
+	setup_tap "$FIB0" inet ${ADDR0} $MASK
+	ifconfig $TAP mtu 9000
+
+	atf_check -s exit:0 -o ignore setfib $FIB0 route change \
+	    ${SUBNET}/${MASK} -mtu 8723
+
+	# Just searching for "8723" is awful, but the output of 'route get' is
+	# not amenable to parsing
+	atf_check -o match:8723 setfib $FIB0 route get $ADDR1
+}
+
+ipv4_change_route_without_dest_cleanup()
+{
+	cleanup_ifaces
+}
+
+# Test that a route can be modified with "route change $SUBNET/$MASK" without
+# needing to also specify the gateway of the route.
+atf_test_case ipv6_change_route_without_dest cleanup
+ipv6_change_route_without_dest_head()
+{
+	atf_set "descr" "Test modifying a route without re-specifying its gateway"
+	atf_set "require.user" "root"
+	atf_set "require.config" "fibs"
+}
+
+ipv6_change_route_without_dest_body()
+{
+	# Configure the TAP interfaces to use a RFC5737 nonrouteable addresses
+	# and a non-default fib
+	SUBNET_PREFIX="2001:db8:"
+	SUBNET="${SUBNET_PREFIX}:0"
+	ADDR0="${SUBNET_PREFIX}:1"
+	ADDR1="${SUBNET_PREFIX}:2"
+
+	MASK="64"
+
+	# Check system configuration
+	if [ 0 != `sysctl -n net.add_addr_allfibs` ]; then
+		atf_skip "This test requires net.add_addr_allfibs=0"
+	fi
+	get_fibs 1
+
+	setup_tap "$FIB0" inet6 ${ADDR0} $MASK
+	ifconfig $TAP mtu 9000
+
+	atf_check -s exit:0 -o ignore setfib $FIB0 route -6 change \
+	    ${SUBNET}/${MASK} -mtu 8723
+
+	# Just searching for "8723" is awful, but the output of 'route get' is
+	# not amenable to parsing
+	atf_check -o match:8723 setfib $FIB0 route -6 get $ADDR1
+}
+
+ipv6_change_route_without_dest_cleanup()
+{
+	cleanup_ifaces
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case arpresolve_checks_interface_fib
@@ -815,6 +901,8 @@
 	atf_add_test_case udp_dontroute6
 	atf_add_test_case ipv4_move_subnet_route
 	atf_add_test_case ipv6_move_subnet_route
+	atf_add_test_case ipv4_change_route_without_dest
+	atf_add_test_case ipv6_change_route_without_dest
 }
 
 # Looks up one or more fibs from the configuration data and validates them.