diff --git a/lib/Lex/TokenConcatenation.cpp b/lib/Lex/TokenConcatenation.cpp
index 30dc8f1..0a66bba 100644
--- a/lib/Lex/TokenConcatenation.cpp
+++ b/lib/Lex/TokenConcatenation.cpp
@@ -12,9 +12,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Lex/TokenConcatenation.h"
+#include "clang/Basic/CharInfo.h"
 #include "clang/Lex/Preprocessor.h"
 #include "llvm/Support/ErrorHandling.h"
-#include <cctype>
 using namespace clang;
 
 
@@ -240,13 +240,12 @@
     return IsIdentifierStringPrefix(PrevTok);
 
   case tok::numeric_constant:
-    return isalnum(FirstChar) || Tok.is(tok::numeric_constant) ||
-           FirstChar == '+' || FirstChar == '-' || FirstChar == '.' ||
-           (PP.getLangOpts().CPlusPlus11 && FirstChar == '_');
+    return isPreprocessingNumberBody(FirstChar) ||
+           FirstChar == '+' || FirstChar == '-';
   case tok::period:          // ..., .*, .1234
     return (FirstChar == '.' && PrevPrevTok.is(tok::period)) ||
-    isdigit(FirstChar) ||
-    (PP.getLangOpts().CPlusPlus && FirstChar == '*');
+           isDigit(FirstChar) ||
+           (PP.getLangOpts().CPlusPlus && FirstChar == '*');
   case tok::amp:             // &&
     return FirstChar == '&';
   case tok::plus:            // ++
diff --git a/test/Preprocessor/output_paste_avoid.c b/test/Preprocessor/output_paste_avoid.cpp
similarity index 73%
rename from test/Preprocessor/output_paste_avoid.c
rename to test/Preprocessor/output_paste_avoid.cpp
index 6defd12..689d966 100644
--- a/test/Preprocessor/output_paste_avoid.c
+++ b/test/Preprocessor/output_paste_avoid.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -E %s -o - | FileCheck -strict-whitespace %s
+// RUN: %clang_cc1 -E -std=c++11 %s -o - | FileCheck -strict-whitespace %s
 
 
 #define y(a) ..a
@@ -37,3 +37,11 @@
 #define TYPEDEF(guid)   typedef [uuid(guid)]
 TYPEDEF(66504301-BE0F-101A-8BBB-00AA00300CAB) long OLE_COLOR;
 // CHECK: typedef [uuid(66504301-BE0F-101A-8BBB-00AA00300CAB)] long OLE_COLOR;
+
+// Be careful with UD-suffixes.
+#define StrSuffix() "abc"_suffix
+#define IntSuffix() 123_suffix
+UD: StrSuffix()ident
+UD: IntSuffix()ident
+// CHECK: UD: "abc"_suffix ident
+// CHECK: UD: 123_suffix ident