Index: lib/Lex/LiteralSupport.cpp
===================================================================
--- lib/Lex/LiteralSupport.cpp	(revision 150006)
+++ lib/Lex/LiteralSupport.cpp	(working copy)
@@ -546,22 +546,27 @@
   // 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);
+    bool noSignificand = (s == DigitsBegin);
     if (s == ThisTokEnd) {
       // Done.
     } else if (*s == '.') {
       s++;
       saw_period = true;
+      const char *floatDigitsBegin = s;
       s = SkipHexDigits(s);
+      noSignificand &= (floatDigitsBegin == s);
     }
+
+    if (noSignificand) {
+      PP.Diag(PP.AdvanceToTokenCharacter(TokLoc, s-ThisTokBegin), \
+        diag::err_hexconstant_requires_digits);
+      hadError = true;
+      return;
+    }
+
     // A binary exponent can appear with or with a '.'. If dotted, the
     // binary exponent is required.
     if (*s == 'p' || *s == 'P') {
Index: test/Lexer/hexfloat.cpp
===================================================================
--- test/Lexer/hexfloat.cpp	(revision 150006)
+++ test/Lexer/hexfloat.cpp	(working copy)
@@ -2,4 +2,6 @@
 // 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 significand}}
-
+double d = 0x.2p2; // expected-warning{{hexadecimal floating constants are a C99 feature}}
+float g = 0x1.2p2; // expected-warning{{hexadecimal floating constants are a C99 feature}}
+double h = 0x1.p2; // expected-warning{{hexadecimal floating constants are a C99 feature}}