diff --git a/gso/workflows/iptrunk/modify_trunk_interface.py b/gso/workflows/iptrunk/modify_trunk_interface.py
index 8394170f7d983da26d125ba3d0a95a749937d49e..1dcda4fd5ceb2f3b2a4114533ff313a76823ac53 100644
--- a/gso/workflows/iptrunk/modify_trunk_interface.py
+++ b/gso/workflows/iptrunk/modify_trunk_interface.py
@@ -32,6 +32,7 @@ from gso.utils.helpers import (
     get_router_vendor,
     validate_interface_name_list,
     validate_iptrunk_unique_interface,
+    validate_tt_number,
 )
 
 
@@ -91,6 +92,10 @@ def initial_input_form_generator(subscription_id: UUIDstr) -> FormGenerator:
         iptrunk_ipv4_network: ipaddress.IPv4Network = ReadOnlyField(subscription.iptrunk.iptrunk_ipv4_network)
         iptrunk_ipv6_network: ipaddress.IPv6Network = ReadOnlyField(subscription.iptrunk.iptrunk_ipv6_network)
 
+        @validator("tt_number", allow_reuse=True)
+        def validate_tt_number(cls, tt_number: str) -> str:
+            return validate_tt_number(tt_number)
+
     initial_user_input = yield ModifyIptrunkForm
     ae_members_side_a = initialize_ae_members(subscription, initial_user_input.dict(), 0)