diff --git a/intl/plural.y b/intl/plural.y
index e02e74541c..2ee128ba01 100644
--- a/intl/plural.y
+++ b/intl/plural.y
@@ -40,6 +40,11 @@
 # define __gettextparse PLURAL_PARSE
 #endif
 
+/* Later we provide those prototypes.  Without these macros, bison may
+   generate its own prototypes with possible conflicts.  */
+#define YYLEX_IS_DECLARED
+#define YYERROR_IS_DECLARED
+
 %}
 %parse-param {struct parse_args *arg}
 %lex-param {struct parse_args *arg}