diff --git a/libstdc++-v3/config/locale/generic/ctype_members.cc b/libstdc++-v3/config/locale/generic/ctype_members.cc
index 2d61347feb1..21c25a68915 100644
--- a/libstdc++-v3/config/locale/generic/ctype_members.cc
+++ b/libstdc++-v3/config/locale/generic/ctype_members.cc
@@ -53,6 +53,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   { }
 
 #ifdef _GLIBCXX_USE_WCHAR_T
+
+  // Values which index into _M_bit and _M_wmask for each classifier
+  enum {
+    _id_alnum, _id_alpha, _id_blank, _id_cntrl,
+    _id_digit, _id_graph, _id_lower, _id_print,
+    _id_punct, _id_space, _id_upper, _id_xdigit,
+    _id_num,
+  };
+
   ctype<wchar_t>::__wmask_type
   ctype<wchar_t>::_M_convert_to_wmask(const mask __m) const throw()
   {
@@ -138,11 +147,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   do_is(mask __m, char_type __c) const
   {
     bool __ret = false;
-    // Generically, 15 (instead of 11) since we don't know the numerical
-    // encoding of the various categories in /usr/include/ctype.h.
-    const size_t __bitmasksize = 15;
-    for (size_t __bitcur = 0; __bitcur <= __bitmasksize; ++__bitcur)
-      if (__m & _M_bit[__bitcur]
+
+    // Each _M_bit may have more than one bit set. Only check tests for which
+    // all of the matching _M_bit values are set. This skips tests with some
+    // bits which are not set. For example:
+    //
+    //  alpha = lower|upper
+    //  __c = 'a'
+    //  __m = upper
+    //
+    // We evaluate iswupper (which returns false), but we skip iswalpha (which
+    // would return true) because __m is missing the lower bit, so the return
+    // value is false.
+    for (size_t __bitcur = 0; __bitcur <= _id_num; ++__bitcur)
+      if ((__m & _M_bit[__bitcur]) == _M_bit[__bitcur]
 	  && iswctype(__c, _M_wmask[__bitcur]))
 	{
 	  __ret = true;
@@ -157,13 +175,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   {
     for (;__lo < __hi; ++__vec, ++__lo)
       {
-	// Generically, 15 (instead of 11) since we don't know the numerical
-	// encoding of the various categories in /usr/include/ctype.h.
-	const size_t __bitmasksize = 15;
-	mask __m = 0;
-	for (size_t __bitcur = 0; __bitcur <= __bitmasksize; ++__bitcur)
-	  if (iswctype(*__lo, _M_wmask[__bitcur]))
-	    __m |= _M_bit[__bitcur];
+
+	// Start with all bits set. Iterate over all wctypes, clearing bits for
+	// non-matching values. For example:
+	//
+	//  alpha == lower|upper
+	//  *__lo == 'a'
+	//
+	//  __m = <all bits>
+	//  iswalpha and iswlower match
+	//    __m left alone
+	//  iswupper does not match
+	//    __m &= ~upper
+	//
+	// The return value will satisfy the following conditions:
+	//
+	//  (__m & alpha) != 0
+	//  (__m & lower) != 0
+	//  (__m & upper) == 0
+	mask __m = (alnum|alpha|blank|cntrl|digit|graph|
+		    lower|print|punct|space|upper|xdigit);
+	for (size_t __bitcur = 0; __bitcur < _id_num; ++__bitcur)
+	  if (!iswctype(*__lo, _M_wmask[__bitcur]))
+	    __m &= ~_M_bit[__bitcur];
 	*__vec = __m;
       }
     return __hi;
@@ -264,11 +298,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	 __i < sizeof(_M_widen) / sizeof(wint_t); ++__i)
       _M_widen[__i] = btowc(__i);
 
-    for (size_t __i = 0; __i <= 15; ++__i)
-      {
-	_M_bit[__i] = static_cast<mask>(1 << __i);
-	_M_wmask[__i] = _M_convert_to_wmask(_M_bit[__i]);
-      }
+    // Set these directly from the OS provided values.
+    // We can't simply iterate over bit values because
+    // they may have more than one bit set
+    _M_bit[_id_alnum] = alnum;
+    _M_bit[_id_alpha] = alpha;
+    _M_bit[_id_blank] = blank;
+    _M_bit[_id_cntrl] = cntrl;
+    _M_bit[_id_digit] = digit;
+    _M_bit[_id_graph] = graph;
+    _M_bit[_id_lower] = lower;
+    _M_bit[_id_print] = print;
+    _M_bit[_id_punct] = punct;
+    _M_bit[_id_space] = space;
+    _M_bit[_id_upper] = upper;
+    _M_bit[_id_xdigit] = xdigit;
+
+    for (size_t __i = 0; __i <= _id_num; __i++)
+      _M_wmask[__i] = _M_convert_to_wmask(_M_bit[__i]);
   }
 #endif //  _GLIBCXX_USE_WCHAR_T