Index: lib/Lex/LiteralSupport.cpp
===================================================================
--- lib/Lex/LiteralSupport.cpp	(revision 148238)
+++ lib/Lex/LiteralSupport.cpp	(working copy)
@@ -538,6 +538,12 @@
   // Handle a hex number like 0x1234.
   if ((*s == 'x' || *s == 'X') && (isxdigit(s[1]) || s[1] == '.')) {
     s++;
+    if (!isxdigit(*s)) {
+      PP.Diag(PP.AdvanceToTokenCharacter(TokLoc, s-ThisTokBegin), \
+	      diag::err_hexconstant_requires_digits);
+      hadError = true;
+      return;
+    }
     radix = 16;
     DigitsBegin = s;
     s = SkipHexDigits(s);
Index: test/Lexer/hexfloat.cpp
===================================================================
--- test/Lexer/hexfloat.cpp	(revision 148238)
+++ test/Lexer/hexfloat.cpp	(working copy)
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -pedantic %s
 // RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify -pedantic %s
 float f = 0x1p+1; // expected-warning{{hexadecimal floating constants are a C99 feature}}
+double e = 0x.p0; //expected-error{{hexadecimal floating constants require a number}}
 
Index: include/clang/Basic/DiagnosticLexKinds.td
===================================================================
--- include/clang/Basic/DiagnosticLexKinds.td	(revision 148238)
+++ include/clang/Basic/DiagnosticLexKinds.td	(working copy)
@@ -111,6 +111,8 @@
 def ext_imaginary_constant : Extension<"imaginary constants are an extension">;
 def err_hexconstant_requires_exponent : Error<
   "hexadecimal floating constants require an exponent">;
+def err_hexconstant_requires_digits : Error<
+  "hexadecimal floating constants require a number">;
 def ext_hexconstant_invalid : Extension<
   "hexadecimal floating constants are a C99 feature">;
 def ext_binary_literal : Extension<