diff --git a/include/uchar.h b/include/uchar.h
--- a/include/uchar.h
+++ b/include/uchar.h
@@ -32,6 +32,11 @@
 #include <sys/cdefs.h>
 #include <sys/_types.h>
 
+#if __ISO_C_VISIBLE >= 2023 && !defined(_CHAR8_T_DECLARED)
+typedef unsigned char	char8_t;
+#define	_CHAR8_T_DECLARED
+#endif
+
 #ifndef _CHAR16_T_DECLARED
 typedef	__char16_t	char16_t;
 #define	_CHAR16_T_DECLARED
diff --git a/sys/sys/stdatomic.h b/sys/sys/stdatomic.h
--- a/sys/sys/stdatomic.h
+++ b/sys/sys/stdatomic.h
@@ -54,6 +54,9 @@
 #ifdef __GCC_ATOMIC_CHAR_LOCK_FREE
 #define	ATOMIC_CHAR_LOCK_FREE		__GCC_ATOMIC_CHAR_LOCK_FREE
 #endif
+#if __ISO_C_VISIBLE >= 2023 && defined(__GCC_ATOMIC_CHAR8_T_LOCK_FREE)
+#define	ATOMIC_CHAR8_T_LOCK_FREE	__GCC_ATOMIC_CHAR8_T_LOCK_FREE
+#endif
 #ifdef __GCC_ATOMIC_CHAR16_T_LOCK_FREE
 #define	ATOMIC_CHAR16_T_LOCK_FREE	__GCC_ATOMIC_CHAR16_T_LOCK_FREE
 #endif
@@ -199,6 +202,9 @@
 typedef _Atomic(unsigned long)		atomic_ulong;
 typedef _Atomic(long long)		atomic_llong;
 typedef _Atomic(unsigned long long)	atomic_ullong;
+#if __ISO_C_VISIBLE >= 2023
+typedef _Atomic(unsigned char)		atomic_char8_t;
+#endif
 typedef _Atomic(__char16_t)		atomic_char16_t;
 typedef _Atomic(__char32_t)		atomic_char32_t;
 typedef _Atomic(___wchar_t)		atomic_wchar_t;