Index: clang/lib/Headers/stdatomic.h
===================================================================
--- clang/lib/Headers/stdatomic.h
+++ clang/lib/Headers/stdatomic.h
@@ -15,10 +15,12 @@
  *
  * Exclude the MSVC path as well as the MSVC header as of the 14.31.30818
  * explicitly disallows `stdatomic.h` in the C mode via an `#error`.  Fallback
- * to the clang resource header until that is fully supported.
+ * to the clang resource header until that is fully supported.  The
+ * `stdatomic.h` header requires C++ 23 or newer.
  */
 #if __STDC_HOSTED__ &&                                                         \
-    __has_include_next(<stdatomic.h>) && !(defined(_MSC_VER) && !defined(__cplusplus))
+    __has_include_next(<stdatomic.h>) &&                                       \
+    !(defined(_MSC_VER) && defined(__cplusplus) && __cplusplus < 202002l)
 # include_next <stdatomic.h>
 #else