diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 3d4a6da469..d8c80325f6 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3645,20 +3645,20 @@ qemuBuildHostNetStr(virDomainNetDefPtr net,
             for (i = 0; i < net->guestIP.nips; i++) {
                 const virNetDevIPAddr *ip = net->guestIP.ips[i];
                 g_autofree char *addr = NULL;
-                const char *prefix = "";
 
                 if (!(addr = virSocketAddrFormat(&ip->address)))
                     return NULL;
 
-                if (VIR_SOCKET_ADDR_IS_FAMILY(&ip->address, AF_INET))
-                    prefix = "net=";
-                if (VIR_SOCKET_ADDR_IS_FAMILY(&ip->address, AF_INET6))
-                    prefix = "ipv6-net=";
-
-                virBufferAsprintf(&buf, "%s%s", prefix, addr);
-                if (ip->prefix)
-                    virBufferAsprintf(&buf, "/%u", ip->prefix);
-                virBufferAddChar(&buf, ',');
+                if (VIR_SOCKET_ADDR_IS_FAMILY(&ip->address, AF_INET)) {
+                    virBufferAsprintf(&buf, "net=%s", addr);
+                    if (ip->prefix)
+                        virBufferAsprintf(&buf, "/%u", ip->prefix);
+                    virBufferAddChar(&buf, ',');
+                } else if (VIR_SOCKET_ADDR_IS_FAMILY(&ip->address, AF_INET6)) {
+                    virBufferAsprintf(&buf, "ipv6-prefix=%s,", addr);
+                    if (ip->prefix)
+                        virBufferAsprintf(&buf, "ipv6-prefixlen=%u,", ip->prefix);
+                }
             }
         }
         break;
diff --git a/tests/qemuxml2argvdata/net-user-addr.args b/tests/qemuxml2argvdata/net-user-addr.args
index 6cc82d9e62..5f1de305e0 100644
--- a/tests/qemuxml2argvdata/net-user-addr.args
+++ b/tests/qemuxml2argvdata/net-user-addr.args
@@ -27,6 +27,7 @@ server,nowait \
 -usb \
 -drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-ide0-0-0 \
 -device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 \
--netdev user,net=172.17.2.0/24,ipv6-net=2001:db8:ac10:fd01::/64,id=hostnet0 \
+-netdev user,net=172.17.2.0/24,ipv6-prefix=2001:db8:ac10:fd01::,\
+ipv6-prefixlen=64,id=hostnet0 \
 -device rtl8139,netdev=hostnet0,id=net0,mac=00:11:22:33:44:55,bus=pci.0,\
 addr=0x3