diff --git a/dlls/user32/class.c b/dlls/user32/class.c
index 51e6faf462e..e94cd2bba0d 100644
--- a/dlls/user32/class.c
+++ b/dlls/user32/class.c
@@ -135,7 +135,7 @@ static BOOL set_server_info( HWND hwnd, INT offset, LONG_PTR newval, UINT size )
         {
         case GCW_ATOM:
             req->flags = SET_CLASS_ATOM;
-            req->atom = newval;
+            req->atom = LOWORD(newval);
         case GCL_STYLE:
             req->flags = SET_CLASS_STYLE;
             req->style = newval;
diff --git a/include/wine/server_protocol.h b/include/wine/server_protocol.h
index 8c958ed4449..727d22c8749 100644
--- a/include/wine/server_protocol.h
+++ b/include/wine/server_protocol.h
@@ -17,7 +17,7 @@
 
 typedef unsigned int obj_handle_t;
 typedef unsigned int user_handle_t;
-typedef unsigned short atom_t;
+typedef unsigned int atom_t;
 typedef unsigned int process_id_t;
 typedef unsigned int thread_id_t;
 typedef unsigned int data_size_t;
@@ -148,7 +148,7 @@ typedef __int64 timeout_t;
 typedef struct
 {
     atom_t         atom;
-    short          string;
+    int            string;
     lparam_t       data;
 } property_data_t;
 
@@ -2857,7 +2857,7 @@ struct get_window_info_reply
     process_id_t   pid;
     thread_id_t    tid;
     atom_t         atom;
-    short int      is_unicode;
+    int            is_unicode;
 };
 
 
@@ -5061,6 +5061,6 @@ union generic_reply
     struct set_window_layered_info_reply set_window_layered_info_reply;
 };
 
-#define SERVER_PROTOCOL_VERSION 376
+#define SERVER_PROTOCOL_VERSION 377
 
 #endif /* __WINE_WINE_SERVER_PROTOCOL_H */
diff --git a/server/protocol.def b/server/protocol.def
index 996d7909c07..e14aefe3cec 100644
--- a/server/protocol.def
+++ b/server/protocol.def
@@ -33,7 +33,7 @@
 
 typedef unsigned int obj_handle_t;
 typedef unsigned int user_handle_t;
-typedef unsigned short atom_t;
+typedef unsigned int atom_t;
 typedef unsigned int process_id_t;
 typedef unsigned int thread_id_t;
 typedef unsigned int data_size_t;
@@ -164,7 +164,7 @@ typedef __int64 timeout_t;
 typedef struct
 {
     atom_t         atom;     /* property atom */
-    short          string;   /* was atom a string originally? */
+    int            string;   /* was atom a string originally? */
     lparam_t       data;     /* data stored in property */
 } property_data_t;
 
@@ -2106,7 +2106,7 @@ enum message_type
     process_id_t   pid;         /* process owning the window */
     thread_id_t    tid;         /* thread owning the window */
     atom_t         atom;        /* class atom */
-    short int      is_unicode;  /* ANSI or unicode */
+    int            is_unicode;  /* ANSI or unicode */
 @END
 
 
diff --git a/tools/make_requests b/tools/make_requests
index 90203aedbaf..31301ce75c3 100755
--- a/tools/make_requests
+++ b/tools/make_requests
@@ -31,7 +31,7 @@ my %formats =
     "unsigned int"  => [  4,   4,  "%08x" ],
     "data_size_t"   => [  4,   4,  "%u" ],
     "obj_handle_t"  => [  4,   4,  "%04x" ],
-    "atom_t"        => [  2,   2,  "%04x" ],
+    "atom_t"        => [  4,   4,  "%04x" ],
     "user_handle_t" => [  4,   4,  "%08x" ],
     "process_id_t"  => [  4,   4,  "%04x" ],
     "thread_id_t"   => [  4,   4,  "%04x" ],