diff --git a/libcxx/include/cstddef b/libcxx/include/cstddef
index 7ef16ff..0030ec2 100644
--- a/libcxx/include/cstddef
+++ b/libcxx/include/cstddef
@@ -52,7 +52,12 @@
 using ::ptrdiff_t;
 using ::size_t;
 
+#if defined(__CLANG_MAX_ALIGN_T_DEFINED) || defined(_GCC_MAX_ALIGN_T)
+// Re-use the compiler's <stddef.h> max_align_t where possible.
+using ::max_align_t;
+#else
 typedef long double max_align_t;
+#endif
 
 #ifdef _LIBCPP_HAS_NO_NULLPTR