diff --git a/libcxx/include/__locale b/libcxx/include/__locale
--- a/libcxx/include/__locale
+++ b/libcxx/include/__locale
@@ -452,7 +452,7 @@
     static const mask punct  = _PUNCT;
     static const mask xdigit = _HEX;
     static const mask blank  = _BLANK;
-    static const mask __regex_word = 0x80;
+    static const mask __regex_word = 0x4000; // 0x8000 and 0x0100 and 0x00ff are used
 # define _LIBCPP_CTYPE_MASK_IS_COMPOSITE_PRINT
 #elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__EMSCRIPTEN__) || defined(__NetBSD__)
 # ifdef __APPLE__
diff --git a/libcxx/test/std/re/re.traits/isctype.pass.cpp b/libcxx/test/std/re/re.traits/isctype.pass.cpp
--- a/libcxx/test/std/re/re.traits/isctype.pass.cpp
+++ b/libcxx/test/std/re/re.traits/isctype.pass.cpp
@@ -6,7 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// XFAIL: LIBCXX-WINDOWS-FIXME
 // XFAIL: LIBCXX-AIX-FIXME
 
 // <regex>
diff --git a/libcxx/test/std/re/re.traits/lookup_classname.pass.cpp b/libcxx/test/std/re/re.traits/lookup_classname.pass.cpp
--- a/libcxx/test/std/re/re.traits/lookup_classname.pass.cpp
+++ b/libcxx/test/std/re/re.traits/lookup_classname.pass.cpp
@@ -6,7 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// XFAIL: LIBCXX-WINDOWS-FIXME
 // XFAIL: LIBCXX-AIX-FIXME
 
 // <regex>
@@ -23,6 +22,16 @@
 #include "test_macros.h"
 #include "test_iterators.h"
 
+// TODO: Move the assert to include/__locale when it passes on all platforms.
+static_assert((std::ctype_base::__regex_word &
+               ~(std::ctype_base::space | std::ctype_base::print |
+                 std::ctype_base::cntrl | std::ctype_base::upper |
+                 std::ctype_base::lower | std::ctype_base::alpha |
+                 std::ctype_base::digit | std::ctype_base::punct |
+                 std::ctype_base::xdigit | std::ctype_base::blank)) ==
+              std::ctype_base::__regex_word,
+              "__regex_word can't overlap other bits");
+
 template <class char_type>
 void
 test(const char_type* A,