diff --git a/lib/Lex/LiteralSupport.cpp b/lib/Lex/LiteralSupport.cpp
index c178d21..a3f97d9 100644
--- a/lib/Lex/LiteralSupport.cpp
+++ b/lib/Lex/LiteralSupport.cpp
@@ -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') {