diff --git a/unstable/wlr-foreign-toplevel-management-unstable-v1.xml b/unstable/wlr-foreign-toplevel-management-unstable-v1.xml
index 44505bb..f5423ab 100644
--- a/unstable/wlr-foreign-toplevel-management-unstable-v1.xml
+++ b/unstable/wlr-foreign-toplevel-management-unstable-v1.xml
@@ -25,7 +25,7 @@
     THIS SOFTWARE.
   </copyright>
 
-  <interface name="zwlr_foreign_toplevel_manager_v1" version="3">
+  <interface name="zwlr_foreign_toplevel_manager_v1" version="4">
     <description summary="list and control opened apps">
       The purpose of this protocol is to enable the creation of taskbars
       and docks by providing them with a list of opened applications and
@@ -68,7 +68,7 @@
     </event>
   </interface>
 
-  <interface name="zwlr_foreign_toplevel_handle_v1" version="3">
+  <interface name="zwlr_foreign_toplevel_handle_v1" version="4">
     <description summary="an opened toplevel">
       A zwlr_foreign_toplevel_handle_v1 object represents an opened toplevel
       window. Each app may have multiple opened toplevels.
@@ -266,5 +266,24 @@
       </description>
       <arg name="parent" type="object" interface="zwlr_foreign_toplevel_handle_v1" allow-null="true"/>
     </event>
+
+    <!-- Version 4 additions -->
+
+    <event name="identifier" since="4">
+      <description summary="a stable identifier for a toplevel">
+        This identifier is used to match a zwlr_foreign_toplevel_handle_v1 object to
+        ext_foreign_toplevel_handle_v1 objects.
+
+        If the compositor implements ext_foreign_toplevel_list_v1, this event should
+        be emitted. If supported, the compositor must only send this event when the
+        handle is created.
+
+        The identifier must exactly match the identifier used by
+        ext_foreign_toplevel_handle_v1.identifier for the same toplevel, therefore
+        inheriting all properties and restrictions of the ext identifier.
+      </description>
+
+      <arg name="identifier" type="string"/>
+    </event>
   </interface>
 </protocol>