diff --git a/tools/widl/typegen.c b/tools/widl/typegen.c
index f320f57789a..fbc9f3cc5bd 100644
--- a/tools/widl/typegen.c
+++ b/tools/widl/typegen.c
@@ -1064,7 +1064,8 @@ static unsigned char get_parameter_fc( const var_t *var, int is_return, unsigned
             case TGT_UNION:
             case TGT_USER_TYPE:
             case TGT_RANGE:
-                *flags |= MustFree;
+                *flags |= MustFree | IsSimpleRef;
+                *typestring_offset = ref->typestring_offset;
                 if (!is_in && is_out) server_size = type_memsize( ref );
                 break;
             case TGT_ARRAY: