diff --git a/include/types.h b/include/types.h
index 950b1a46..0ad9ae61 100644
--- a/include/types.h
+++ b/include/types.h
@@ -20,8 +20,11 @@ typedef signed long long s64;
 typedef unsigned long size_t;
 typedef signed long ssize_t;
 
+/* bool, false and true are predefined since C23. */
+#if __STDC_VERSION__ < 202311L
 typedef unsigned char bool;
 #define false	0U
 #define true	1U
+#endif
 
 #endif /* TYPES_H_ */