diff --git a/scripts/mkqtdecl_common/c++.treetop b/scripts/mkqtdecl_common/c++.treetop
index f20cfd293..5eb54c856 100644
--- a/scripts/mkqtdecl_common/c++.treetop
+++ b/scripts/mkqtdecl_common/c++.treetop
@@ -72,6 +72,7 @@ grammar CPP
         "__v16sf" s / 
         "__v16si" s / 
         "decltype" s attribute_value s / 
+        "alignas" s "(" s block s ")" s / 
         "[[" s block s "]]" s )* 
   end