diff --git a/node.h b/node.h
index c6004b8608..cffb174aa5 100644
--- a/node.h
+++ b/node.h
@@ -540,7 +540,7 @@ void *rb_parser_malloc(struct parser_params *, size_t);
 void *rb_parser_realloc(struct parser_params *, void *, size_t);
 void *rb_parser_calloc(struct parser_params *, size_t, size_t);
 void rb_parser_free(struct parser_params *, void *);
-void rb_parser_printf(struct parser_params *parser, const char *fmt, ...);
+PRINTF_ARGS(void rb_parser_printf(struct parser_params *parser, const char *fmt, ...), 2, 3);
 
 RUBY_SYMBOL_EXPORT_END
 
diff --git a/parse.y b/parse.y
index 3515fde47f..f044ae2aff 100644
--- a/parse.y
+++ b/parse.y
@@ -9110,7 +9110,7 @@ parser_token_value_print(struct parser_params *p, enum yytokentype type, const Y
 	break;
       case tBACK_REF:
 #ifndef RIPPER
-	rb_parser_printf(p, "$%c", valp->node->nd_nth);
+	rb_parser_printf(p, "$%c", (int)valp->node->nd_nth);
 #else
 	rb_parser_printf(p, "%"PRIsVALUE, valp->val);
 #endif