diff --git a/server/protocol.def b/server/protocol.def
index 5cb951d..90e943b 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -2131,6 +2131,7 @@
     user_handle_t  parent;        /* parent window */
     atom_t         atom;          /* class atom for the listed children */
     thread_id_t    tid;           /* thread owning the listed children */
+    VARARG(class,unicode_str);    /* class name */
 @REPLY
     int            count;         /* total count of children */
     VARARG(children,user_handles); /* children handles */