diff --git a/include/dix.h b/include/dix.h
index 21176a8c3..921156b4c 100644
--- a/include/dix.h
+++ b/include/dix.h
@@ -80,7 +80,7 @@ SOFTWARE.
 
 #define REQUEST_FIXED_SIZE(req, n)\
     if (((sizeof(req) >> 2) > client->req_len) || \
-        ((n >> 2) >= client->req_len) || \
+        (((n) >> 2) >= client->req_len) ||                              \
         ((((uint64_t) sizeof(req) + (n) + 3) >> 2) != (uint64_t) client->req_len))  \
          return(BadLength)