Index: test/Lexer/cxx-features.cpp
===================================================================
--- test/Lexer/cxx-features.cpp	(revision 220262)
+++ test/Lexer/cxx-features.cpp	(working copy)
@@ -16,6 +16,10 @@
 #error "wrong value for __cpp_binary_literals"
 #endif
 
+#if check(digit_separators, 0, 0, 201309)
+#error "wrong value for __cpp_digit_separators"
+#endif
+
 #if check(init_captures, 0, 0, 201304)
 #error "wrong value for __cpp_init_captures"
 #endif
Index: docs/LanguageExtensions.rst
===================================================================
--- docs/LanguageExtensions.rst	(revision 220262)
+++ docs/LanguageExtensions.rst	(working copy)
@@ -751,6 +751,12 @@
 ``__has_extension(cxx_aggregate_nsdmi)`` to determine if support
 for default initializers in aggregate members is enabled.
 
+C++1y digit separators
+^^^^^^^^^^^^^^^^^^^^^^
+
+Use ``__cpp_digit_separators`` to determine if support for digit separators
+using single quotes (for instance, ``10'000``) is enabled.
+
 C++1y generalized lambda capture
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
Index: lib/Frontend/InitPreprocessor.cpp
===================================================================
--- lib/Frontend/InitPreprocessor.cpp	(revision 220262)
+++ lib/Frontend/InitPreprocessor.cpp	(working copy)
@@ -428,6 +428,7 @@
   // C++14 features.
   if (LangOpts.CPlusPlus14) {
     Builder.defineMacro("__cpp_binary_literals", "201304");
+    Builder.defineMacro("__cpp_digit_separators", "201309");
     Builder.defineMacro("__cpp_init_captures", "201304");
     Builder.defineMacro("__cpp_generic_lambdas", "201304");
     Builder.defineMacro("__cpp_decltype_auto", "201304");