diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index d5a4643..d82f8fc 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -724,7 +724,8 @@
     return LexNumericConstant(Result, ConsumeChar(CurPtr, Size, Result));
 
   // If we have a hex FP constant, continue.
-  if ((C == '-' || C == '+') && (PrevCh == 'P' || PrevCh == 'p'))
+  if ((C == '-' || C == '+') && (PrevCh == 'P' || PrevCh == 'p') &&
+      (!PP || !PP->getLangOptions().CPlusPlus0x))
     return LexNumericConstant(Result, ConsumeChar(CurPtr, Size, Result));
 
   // Update the location of token as well as BufferPtr.
diff --git a/clang/lib/Lex/LiteralSupport.cpp b/clang/lib/Lex/LiteralSupport.cpp
index 9aaa82d..5cd5497 100644
--- a/clang/lib/Lex/LiteralSupport.cpp
+++ b/clang/lib/Lex/LiteralSupport.cpp
@@ -458,7 +458,7 @@
     }
     // A binary exponent can appear with or with a '.'. If dotted, the
     // binary exponent is required.
-    if (*s == 'p' || *s == 'P') {
+    if ((*s == 'p' || *s == 'P') && !PP.getLangOptions().CPlusPlus0x) {
       const char *Exponent = s;
       s++;
       saw_exponent = true;
@@ -472,7 +472,12 @@
       }
       s = first_non_digit;
 
-      if (!PP.getLangOptions().HexFloats)
+      // In C++0x, we cannot support hexadecmial floating literals because
+      // they conflict with user-defined literals, so we warn in previous
+      // versions of C++ by default.
+      if (PP.getLangOptions().CPlusPlus)
+        PP.Diag(TokLoc, diag::ext_hexconstant_cplusplus);
+      else if (!PP.getLangOptions().HexFloats)
         PP.Diag(TokLoc, diag::ext_hexconstant_invalid);
     } else if (saw_period) {
       PP.Diag(PP.AdvanceToTokenCharacter(TokLoc, s-ThisTokBegin),