diff --git a/data/api/client-server/administrative_contact.yaml b/data/api/client-server/administrative_contact.yaml
index 2ce11e531..eddb2b01a 100644
--- a/data/api/client-server/administrative_contact.yaml
+++ b/data/api/client-server/administrative_contact.yaml
@@ -120,7 +120,6 @@ paths:
                       description: The client secret used in the session with the identity server.
                     id_server:
                       type: string
-                      format: mx-server-name
                       description: The identity server to use.
                     id_access_token:
                       type: string
@@ -280,7 +279,6 @@ paths:
                   description: The client secret used in the session with the identity server.
                 id_server:
                   type: string
-                  format: mx-server-name
                   description: The identity server to use.
                 id_access_token:
                   type: string
@@ -340,7 +338,6 @@ paths:
               properties:
                 id_server:
                   type: string
-                  format: mx-server-name
                   description: |-
                     The identity server to unbind from. If not provided, the homeserver
                     MUST use the `id_server` the identifier was added through. If the
@@ -411,7 +408,6 @@ paths:
               properties:
                 id_server:
                   type: string
-                  format: mx-server-name
                   description: |-
                     The identity server to unbind from. If not provided, the homeserver
                     MUST use the `id_server` the identifier was added through. If the
diff --git a/data/api/client-server/definitions/request_email_validation.yaml b/data/api/client-server/definitions/request_email_validation.yaml
index aa47e6589..d52ea18e9 100644
--- a/data/api/client-server/definitions/request_email_validation.yaml
+++ b/data/api/client-server/definitions/request_email_validation.yaml
@@ -18,7 +18,6 @@ allOf:
   properties:
     id_server:
       type: string
-      format: mx-server-name
       description: |-
         The hostname of the identity server to communicate with. May optionally
         include a port. This parameter is ignored when the homeserver handles
diff --git a/data/api/client-server/definitions/request_msisdn_validation.yaml b/data/api/client-server/definitions/request_msisdn_validation.yaml
index 8d5d73851..fba3a615d 100644
--- a/data/api/client-server/definitions/request_msisdn_validation.yaml
+++ b/data/api/client-server/definitions/request_msisdn_validation.yaml
@@ -18,7 +18,6 @@ allOf:
   properties:
     id_server:
       type: string
-      format: mx-server-name
       description: |-
         The hostname of the identity server to communicate with. May optionally
         include a port. This parameter is ignored when the homeserver handles
diff --git a/data/api/client-server/registration.yaml b/data/api/client-server/registration.yaml
index a2d043059..a418d2d2f 100644
--- a/data/api/client-server/registration.yaml
+++ b/data/api/client-server/registration.yaml
@@ -614,7 +614,6 @@ paths:
                     - $ref: definitions/auth_data.yaml
                 id_server:
                   type: string
-                  format: mx-server-name
                   description: |-
                     The identity server to unbind all of the user's 3PIDs from.
                     If not provided, the homeserver MUST use the `id_server`