diff --git mfbt/Alignment.h mfbt/Alignment.h
index e0843ca..353ec36 100644
--- mozilla/mfbt/Alignment.h
+++ mozilla/mfbt/Alignment.h
@@ -15,6 +15,13 @@
 
 namespace mozilla {
 
+#if defined(MOZ_HAVE_CXX11_ALIGNAS)
+#define MOZ_ALIGNOF(T) alignof(T)
+#elif defined(__GNUC__)
+#define MOZ_ALIGNOF(T) __alignof__(T)
+#elif defined(_MSC_VER)
+#define MOZ_ALIGNOF(T) __alignof(T)
+#else
 /*
  * This class, and the corresponding macro MOZ_ALIGNOF, figures out how many
  * bytes of alignment a given type needs.
@@ -32,6 +41,7 @@ public:
 };
 
 #define MOZ_ALIGNOF(T) mozilla::AlignmentFinder<T>::alignment
+#endif
 
 /*
  * Declare the MOZ_ALIGNED_DECL macro for declaring aligned types.
@@ -43,7 +53,10 @@ public:
  * will declare a two-character array |arr| aligned to 8 bytes.
  */
 
-#if defined(__GNUC__)
+#if defined(MOZ_HAVE_CXX11_ALIGNAS)
+#  define MOZ_ALIGNED_DECL(_type, _align) \
+     alignas(_align) _type
+#elif defined(__GNUC__)
 #  define MOZ_ALIGNED_DECL(_type, _align) \
      _type __attribute__((aligned(_align)))
 #elif defined(_MSC_VER)
diff --git mfbt/Attributes.h mfbt/Attributes.h
index d317766..ddb13da 100644
--- mozilla/mfbt/Attributes.h
+++ mozilla/mfbt/Attributes.h
@@ -50,6 +50,7 @@
  * don't indicate support for them here, due to
  * http://stackoverflow.com/questions/20498142/visual-studio-2013-explicit-keyword-bug
  */
+#  define MOZ_HAVE_CXX11_ALIGNAS
 #  define MOZ_HAVE_NEVER_INLINE          __declspec(noinline)
 #  define MOZ_HAVE_NORETURN              __declspec(noreturn)
 #  ifdef __clang__
@@ -70,6 +71,9 @@
 #  ifndef __has_extension
 #    define __has_extension __has_feature /* compatibility, for older versions of clang */
 #  endif
+#  if __has_extension(cxx_alignas)
+#    define MOZ_HAVE_CXX11_ALIGNAS
+#  endif
 #  if __has_extension(cxx_constexpr)
 #    define MOZ_HAVE_CXX11_CONSTEXPR
 #  endif
@@ -86,6 +90,7 @@
 #  if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
 #    define MOZ_HAVE_CXX11_CONSTEXPR
 #    if MOZ_GCC_VERSION_AT_LEAST(4, 8, 0)
+#      define MOZ_HAVE_CXX11_ALIGNAS
 #      define MOZ_HAVE_CXX11_CONSTEXPR_IN_TEMPLATES
 #    endif
 #    define MOZ_HAVE_EXPLICIT_CONVERSION