-m4_if(b4_prefix, [yy], [],
+m4_if(b4_api_prefix, [yy], [],
+[[/* Substitute the type names. */
+#define YYSTYPE ]b4_api_PREFIX[STYPE
+#define YYSTYPE_IS_TRIVIAL ]b4_api_PREFIX[STYPE_IS_TRIVIAL
+#define YYSTYPE_IS_DECLARED ]b4_api_PREFIX[STYPE_IS_DECLARED]b4_locations_if([[
+#define YYLTYPE ]b4_api_PREFIX[LTYPE
+#define YYLTYPE_IS_TRIVIAL ]b4_api_PREFIX[LTYPE_IS_TRIVIAL
+#define YYLTYPE_IS_DECLARED ]b4_api_PREFIX[LTYPE_IS_DECLARED]])])[
+]m4_if(b4_prefix, [yy], [],