Index: libcxx/trunk/include/cstddef
===================================================================
--- libcxx/trunk/include/cstddef
+++ libcxx/trunk/include/cstddef
@@ -48,7 +48,8 @@
 using ::ptrdiff_t;
 using ::size_t;
 
-#if defined(__CLANG_MAX_ALIGN_T_DEFINED) || defined(_GCC_MAX_ALIGN_T)
+#if defined(__CLANG_MAX_ALIGN_T_DEFINED) || defined(_GCC_MAX_ALIGN_T) || \
+    defined(__DEFINED_max_align_t)
 // Re-use the compiler's <stddef.h> max_align_t where possible.
 using ::max_align_t;
 #else
Index: libcxx/trunk/include/stddef.h
===================================================================
--- libcxx/trunk/include/stddef.h
+++ libcxx/trunk/include/stddef.h
@@ -53,7 +53,8 @@
 }
 
 // Re-use the compiler's <stddef.h> max_align_t where possible.
-#if !defined(__CLANG_MAX_ALIGN_T_DEFINED) && !defined(_GCC_MAX_ALIGN_T)
+#if !defined(__CLANG_MAX_ALIGN_T_DEFINED) && !defined(_GCC_MAX_ALIGN_T) && \
+    !defined(__DEFINED_max_align_t)
 typedef long double max_align_t;
 #endif