Index: lib/Lex/LiteralSupport.cpp
===================================================================
--- lib/Lex/LiteralSupport.cpp
+++ lib/Lex/LiteralSupport.cpp
@@ -751,7 +751,8 @@
 
   // If we have a hex digit other than 'e' (which denotes a FP exponent) then
   // the code is using an incorrect base.
-  if (isHexDigit(*s) && *s != 'e' && *s != 'E') {
+  if (isHexDigit(*s) && *s != 'e' && *s != 'E' &&
+      !isValidUDSuffix(PP.getLangOpts(), StringRef(s, ThisTokEnd - s))) {
     PP.Diag(PP.AdvanceToTokenCharacter(TokLoc, s-ThisTokBegin),
             diag::err_invalid_digit) << StringRef(s, 1) << (radix == 8 ? 1 : 0);
     hadError = true;
@@ -804,12 +805,14 @@
   if (!LangOpts.CPlusPlus14)
     return false;
 
-  // In C++1y, "s", "h", "min", "ms", "us", and "ns" are used in the library.
+  // In C++14, "s", "h", "min", "ms", "us", and "ns" are used in the library.
   // Per tweaked N3660, "il", "i", and "if" are also used in the library.
+  // In C++2a "d" and "y" are used in the library.
   return llvm::StringSwitch<bool>(Suffix)
       .Cases("h", "min", "s", true)
       .Cases("ms", "us", "ns", true)
       .Cases("il", "i", "if", true)
+      .Cases("d", "y", LangOpts.CPlusPlus2a)
       .Default(false);
 }
 
@@ -922,7 +925,9 @@
     s = SkipBinaryDigits(s);
     if (s == ThisTokEnd) {
       // Done.
-    } else if (isHexDigit(*s)) {
+    } else if (isHexDigit(*s) &&
+               !isValidUDSuffix(PP.getLangOpts(),
+                                StringRef(s, ThisTokEnd - s))) {
       PP.Diag(PP.AdvanceToTokenCharacter(TokLoc, s-ThisTokBegin),
               diag::err_invalid_digit) << StringRef(s, 1) << 2;
       hadError = true;
Index: test/SemaCXX/cxx2a-user-defined-literals.cpp
===================================================================
--- test/SemaCXX/cxx2a-user-defined-literals.cpp
+++ test/SemaCXX/cxx2a-user-defined-literals.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c++2a %s -include %s -verify
+
+#ifndef INCLUDED
+#define INCLUDED
+
+#pragma clang system_header
+namespace std {
+  namespace chrono {
+    struct day{};
+    struct year{};
+  }
+  constexpr chrono::day operator"" d(unsigned long long d) noexcept;
+  constexpr chrono::year operator"" y(unsigned long long y) noexcept;
+}
+
+#else
+
+using namespace std;
+chrono::day dec_d = 5d;
+chrono::day oct_d = 05d;
+chrono::day bin_d = 0b011d;
+// expected-error@+3{{no viable conversion from 'int' to 'chrono::day'}}
+// expected-note@9{{candidate constructor (the implicit copy constructor)}}
+// expected-note@9{{candidate constructor (the implicit move constructor)}}
+chrono::day hex_d = 0x44d;
+chrono::year y  = 10y;
+#endif