diff --git a/stl/inc/regex b/stl/inc/regex
index 2cfb6d8de33..3c70e9955cd 100644
--- a/stl/inc/regex
+++ b/stl/inc/regex
@@ -298,11 +298,13 @@ public:
     }
 
     bool isctype(_Elem _Ch, char_class_type _Fx) const {
-        if (_Fx != static_cast<char_class_type>(-1)) {
-            return _Getctype()->is(_Fx, _Ch);
-        } else {
+        if (_Fx == static_cast<char_class_type>(_Ch_blank)) {
+            return _Getctype()->is(_SP, _Ch) || _Getctype()->is(_CN, _Ch);
+        } else if (_Fx == static_cast<char_class_type>(-1)) {
             return _Ch == '_' // assumes L'_' == '_'
                    || _Getctype()->is(_Ch_alnum, _Ch);
+        } else {
+            return _Getctype()->is(_Fx, _Ch);
         }
     }
 
diff --git a/stl/inc/xlocale b/stl/inc/xlocale
index 3f2a2a488de..d96bb1afd95 100644
--- a/stl/inc/xlocale
+++ b/stl/inc/xlocale
@@ -2611,6 +2611,9 @@ public:
     using char_type = _Elem;
 
     bool __CLR_OR_THIS_CALL is(mask _Maskval, _Elem _Ch) const { // test if element fits any mask classifications
+        if (_Maskval == blank) {
+            return _isblank_l(_Ch, _get_current_locale()) != 0;
+        }
         return (_Ctype._Table[static_cast<unsigned char>(_Ch)] & _Maskval) != 0;
     }