diff --git a/src/migration-scripts/firewall/5-to-6 b/src/migration-scripts/firewall/5-to-6
index 3fa07a0a1..e1eaea7a1 100755
--- a/src/migration-scripts/firewall/5-to-6
+++ b/src/migration-scripts/firewall/5-to-6
@@ -1,63 +1,105 @@
 #!/usr/bin/env python3
 #
 # Copyright (C) 2021 VyOS maintainers and contributors
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 or later as
 # published by the Free Software Foundation.
 #
 # This program is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 # GNU General Public License for more details.
 #
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 # T3090: migrate "firewall options interface <name> adjust-mss" to the
 #        individual interface.
 
 from sys import argv
 from sys import exit
 
 from vyos.configtree import ConfigTree
 from vyos.ifconfig import Section
 
 if len(argv) < 2:
     print("Must specify file name!")
     exit(1)
 
 file_name = argv[1]
 
 with open(file_name, 'r') as f:
     config_file = f.read()
 
 base = ['firewall', 'options', 'interface']
 config = ConfigTree(config_file)
 
 if not config.exists(base):
     # Nothing to do
     exit(0)
 
 for interface in config.list_nodes(base):
     if config.exists(base + [interface, 'disable']):
         continue
 
     if config.exists(base + [interface, 'adjust-mss']):
         section = Section.section(interface)
         tmp = config.return_value(base + [interface, 'adjust-mss'])
-        config.set(['interfaces', section, interface, 'ip', 'adjust-mss'], value=tmp)
+
+        vlan = interface.split('.')
+        base_interface_path = ['interfaces', section, vlan[0]]
+
+        if len(vlan) == 1:
+            # Normal interface, no VLAN
+            config.set(base_interface_path + ['ip', 'adjust-mss'], value=tmp)
+        elif len(vlan) == 2:
+            # Regular VIF or VIF-S interface - we need to check the config
+            vif = vlan[1]
+            if config.exists(base_interface_path + ['vif', vif]):
+                config.set(base_interface_path + ['vif', vif, 'ip', 'adjust-mss'], value=tmp)
+            elif config.exists(base_interface_path + ['vif-s', vif]):
+                config.set(base_interface_path + ['vif-s', vif, 'ip', 'adjust-mss'], value=tmp)
+        elif len(vlan) == 3:
+            # VIF-S interface with VIF-C subinterface
+            vif_s = vlan[1]
+            vif_c = vlan[2]
+            config.set(base_interface_path + ['vif-s', vif_s, 'vif-c', vif_c, 'ip', 'adjust-mss'], value=tmp)
+            config.set_tag(base_interface_path + ['vif-s'])
+            config.set_tag(base_interface_path + ['vif-s', vif_s, 'vif-c'])
 
     if config.exists(base + [interface, 'adjust-mss6']):
         section = Section.section(interface)
         tmp = config.return_value(base + [interface, 'adjust-mss6'])
-        config.set(['interfaces', section, interface, 'ipv6', 'adjust-mss'], value=tmp)
+
+        vlan = interface.split('.')
+        base_interface_path = ['interfaces', section, vlan[0]]
+
+        if len(vlan) == 1:
+            # Normal interface, no VLAN
+            config.set(['interfaces', section, interface, 'ipv6', 'adjust-mss'], value=tmp)
+        elif len(vlan) == 2:
+            # Regular VIF or VIF-S interface - we need to check the config
+            vif = vlan[1]
+            if config.exists(base_interface_path + ['vif', vif]):
+                config.set(base_interface_path + ['vif', vif, 'ipv6', 'adjust-mss'], value=tmp)
+                config.set_tag(base_interface_path + ['vif'])
+            elif config.exists(base_interface_path + ['vif-s', vif]):
+                config.set(base_interface_path + ['vif-s', vif, 'ipv6', 'adjust-mss'], value=tmp)
+                config.set_tag(base_interface_path + ['vif-s'])
+        elif len(vlan) == 3:
+            # VIF-S interface with VIF-C subinterface
+            vif_s = vlan[1]
+            vif_c = vlan[2]
+            config.set(base_interface_path + ['vif-s', vif_s, 'vif-c', vif_c, 'ipv6', 'adjust-mss'], value=tmp)
+            config.set_tag(base_interface_path + ['vif-s'])
+            config.set_tag(base_interface_path + ['vif-s', vif_s, 'vif-c'])
 
 config.delete(['firewall', 'options'])
 
 try:
     with open(file_name, 'w') as f:
         f.write(config.to_string())
 except OSError as e:
     print("Failed to save the modified config: {}".format(e))
     exit(1)