diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 6715e531f0b..737f89cc8e8 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,8 @@
+2013-08-20  Tim Shen  <timshen91@gmail.com>
+
+	* include/bits/regex_constants.h: Add underlying `unsigned int` for
+	  enum syntax_option_type.
+
 2013-08-18  Tim Shen  <timshen91@gmail.com>
 
 	* include/bits/regex_automaton.h: _S_opcode_backref.
diff --git a/libstdc++-v3/include/bits/regex_constants.h b/libstdc++-v3/include/bits/regex_constants.h
index 6ac65d79913..03e25e2d804 100644
--- a/libstdc++-v3/include/bits/regex_constants.h
+++ b/libstdc++-v3/include/bits/regex_constants.h
@@ -77,7 +77,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    * elements @c ECMAScript, @c basic, @c extended, @c awk, @c grep, @c egrep
    * %set.
    */
-  enum syntax_option_type
+  enum syntax_option_type : unsigned int
     {
       /**
        * Specifies that the matching of regular expressions against a character