diff --git a/dlls/win32u/message.c b/dlls/win32u/message.c
index 3c8be48587a..044310a2f0e 100644
--- a/dlls/win32u/message.c
+++ b/dlls/win32u/message.c
@@ -2729,7 +2729,7 @@ int peek_message( MSG *msg, const struct peek_message_filter *filter )
     {
         NTSTATUS res;
         size_t size = 0;
-        const message_data_t *msg_data = buffer;
+        const union message_data *msg_data = buffer;
         UINT wake_mask, signal_bits, wake_bits, changed_bits, clear_bits = 0;
 
         /* use the same logic as in server/queue.c get_message */
@@ -3320,7 +3320,7 @@ BOOL WINAPI NtUserGetMessage( MSG *msg, HWND hwnd, UINT first, UINT last )
 static BOOL put_message_in_queue( const struct send_message_info *info, size_t *reply_size )
 {
     struct packed_message data;
-    message_data_t msg_data;
+    union message_data msg_data;
     unsigned int res;
     int i;
     timeout_t timeout = TIMEOUT_INFINITE;
diff --git a/include/wine/server_protocol.h b/include/wine/server_protocol.h
index 430ccc965a6..eaff2b66929 100644
--- a/include/wine/server_protocol.h
+++ b/include/wine/server_protocol.h
@@ -344,13 +344,13 @@ typedef union
     } hw;
 } hw_input_t;
 
-typedef union
+union message_data
 {
     unsigned char            bytes[1];
     struct hardware_msg_data hardware;
     struct callback_msg_data callback;
     struct winevent_msg_data winevent;
-} message_data_t;
+};
 
 
 struct filesystem_event
diff --git a/server/protocol.def b/server/protocol.def
index 16f33a3e658..c29a1ff9266 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -360,13 +360,13 @@ typedef union
     } hw;
 } hw_input_t;
 
-typedef union
+union message_data
 {
     unsigned char            bytes[1];   /* raw data for sent messages */
     struct hardware_msg_data hardware;
     struct callback_msg_data callback;
     struct winevent_msg_data winevent;
-} message_data_t;
+};
 
 /* structure returned in filesystem events */
 struct filesystem_event
diff --git a/server/request_handlers.h b/server/request_handlers.h
index d4fbfb34ca7..76ff0abeca7 100644
--- a/server/request_handlers.h
+++ b/server/request_handlers.h
@@ -613,7 +613,6 @@ C_ASSERT( sizeof(ioctl_code_t) == 4 );
 C_ASSERT( sizeof(irp_params_t) == 32 );
 C_ASSERT( sizeof(lparam_t) == 8 );
 C_ASSERT( sizeof(mem_size_t) == 8 );
-C_ASSERT( sizeof(message_data_t) == 48 );
 C_ASSERT( sizeof(mod_handle_t) == 8 );
 C_ASSERT( sizeof(obj_handle_t) == 4 );
 C_ASSERT( sizeof(obj_locator_t) == 16 );
@@ -642,6 +641,7 @@ C_ASSERT( sizeof(timeout_t) == 8 );
 C_ASSERT( sizeof(udp_endpoint) == 32 );
 C_ASSERT( sizeof(union apc_call) == 64 );
 C_ASSERT( sizeof(union apc_result) == 40 );
+C_ASSERT( sizeof(union message_data) == 48 );
 C_ASSERT( sizeof(unsigned __int64) == 8 );
 C_ASSERT( sizeof(unsigned char) == 1 );
 C_ASSERT( sizeof(unsigned int) == 4 );
diff --git a/tools/make_requests b/tools/make_requests
index 2eaffe30c0b..bd69742a9b4 100755
--- a/tools/make_requests
+++ b/tools/make_requests
@@ -47,7 +47,6 @@ my %formats =
     "context_t"                => [  1728,  8 ],
     "cursor_pos_t"             => [  24,  8 ],
     "debug_event_t"            => [  160,  8 ],
-    "message_data_t"           => [  48,  8 ],
     "pe_image_info_t"          => [  88,  8 ],
     "property_data_t"          => [  16,  8 ],
     "select_op_t"              => [  264,  8 ],
@@ -61,6 +60,7 @@ my %formats =
     "struct handle_info"       => [ 20, 4 ],
     "struct luid"              => [  8, 4 ],
     "struct luid_attr"         => [ 12, 4 ],
+    "union message_data"       => [ 48, 8 ],
     "struct object_attributes" => [ 16, 4 ],
     "struct object_type_info"  => [ 44, 4 ],
     "struct process_info"      => [ 40, 8 ],