diff --git a/ext/json/generator/generator.h b/ext/json/generator/generator.h
index 16aae7bc629653..e98588a787b28b 100644
--- a/ext/json/generator/generator.h
+++ b/ext/json/generator/generator.h
@@ -6,9 +6,7 @@
 
 #include "ruby.h"
 
-#ifdef HAVE_STDBOOL_H
-#include <stdbool.h>
-#else
+#ifndef RBIMPL_STDBOOL_H
 /* This is the fallback definition from Ruby 3.0.5. */
 typedef unsigned char _Bool
 #define bool _Bool