diff --git a/libcxx/include/__config b/libcxx/include/__config
index ca6aade34107b..c16552228dbb1 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1198,6 +1198,7 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK
 #  endif
 
+// TODO(LLVM 22): Remove this macro once LLVM19 support ends. __cpp_explicit_this_parameter has been set in LLVM20.
 // Clang-18 has support for deducing this, but it does not set the FTM.
 #  if defined(__cpp_explicit_this_parameter) || (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 1800)
 #    define _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER 1