diff --git a/server/protocol.def b/server/protocol.def
index 80a4af4..02a95c0 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -172,6 +172,21 @@
     int  bottom;
 } rectangle_t;
 
+/* structures for extra message data */
+struct winevent_msg_data
+{
+    user_handle_t   hook;       /* hook handle */
+    thread_id_t     tid;        /* thread id */
+    void           *hook_proc;  /* hook proc address */
+    /* followed by module name if any */
+};
+
+typedef union
+{
+    unsigned char            bytes[1];   /* raw data for sent messages */
+    struct winevent_msg_data winevent;
+} message_data_t;
+
 /* structure for console char/attribute info */
 typedef struct
 {
@@ -1627,13 +1642,11 @@
     unsigned long   info;      /* extra info (callback argument for MSG_CALLBACK_RESULT) */
     int             x;         /* x position */
     int             y;         /* y position */
-    user_handle_t   hook;      /* winevent hook handle */
-    void*           hook_proc; /* winevent hook proc address */
     unsigned int    time;      /* message time */
     unsigned int    hw_id;     /* id if hardware message */
     unsigned int    active_hooks; /* active hooks bitmap */
     data_size_t     total;     /* total size of extra data */
-    VARARG(data,bytes);        /* message data for sent messages */
+    VARARG(data,message_data); /* message data for sent messages */
 @END
 #define GET_MSG_REMOVE      1  /* remove the message */
 #define GET_MSG_SENT_ONLY   2  /* only get sent messages */