Index: libcxx/include/cstddef
===================================================================
--- libcxx/include/cstddef
+++ libcxx/include/cstddef
@@ -49,6 +49,9 @@
 using ::ptrdiff_t;
 using ::size_t;
 
+// max_align_t is part of C99/C++11, but necessary for <new>
+// if the compiler doesn't tell us the default new alignment.
+#if !defined(_LIBCPP_CXX03_LANG) || !defined(__STDCPP_DEFAULT_NEW_ALIGNMENT__)
 #if defined(__CLANG_MAX_ALIGN_T_DEFINED) || defined(_GCC_MAX_ALIGN_T) || \
     defined(__DEFINED_max_align_t) || defined(__NetBSD__)
 // Re-use the compiler's <stddef.h> max_align_t where possible.
@@ -56,6 +59,7 @@
 #else
 typedef long double max_align_t;
 #endif
+#endif
 
 _LIBCPP_END_NAMESPACE_STD