Index: libcxx/include/__threading_support
===================================================================
--- libcxx/include/__threading_support
+++ libcxx/include/__threading_support
@@ -240,6 +240,9 @@
 int __libcpp_tls_create(__libcpp_tls_key* __key,
                         void(_LIBCPP_TLS_DESTRUCTOR_CC* __at_exit)(void*));
 
+_LIBCPP_THREAD_ABI_VISIBILITY
+void __libcpp_tls_destroy(__libcpp_tls_key __key);
+
 _LIBCPP_THREAD_ABI_VISIBILITY
 void *__libcpp_tls_get(__libcpp_tls_key __key);
 
Index: libcxx/src/support/win32/thread_win32.cpp
===================================================================
--- libcxx/src/support/win32/thread_win32.cpp
+++ libcxx/src/support/win32/thread_win32.cpp
@@ -259,6 +259,11 @@
   return 0;
 }
 
+void __libcpp_tls_destroy(__libcpp_tls_key __key)
+{
+  FlsFree(__key);
+}
+
 void *__libcpp_tls_get(__libcpp_tls_key __key)
 {
   return FlsGetValue(__key);
Index: libcxxabi/src/cxa_exception_storage.cpp
===================================================================
--- libcxxabi/src/cxa_exception_storage.cpp
+++ libcxxabi/src/cxa_exception_storage.cpp
@@ -64,9 +64,18 @@
             abort_message("cannot zero out thread value for __cxa_get_globals()");
     }
 
+#if defined(_LIBCPP_HAS_THREAD_API_WIN32)
+    void destroy_() {
+        std::__libcpp_tls_destroy(key_);
+    }
+#endif
+
     void construct_() {
         if (0 != std::__libcpp_tls_create(&key_, destruct_))
             abort_message("cannot create thread specific key for __cxa_get_globals()");
+#if defined(_LIBCPP_HAS_THREAD_API_WIN32)
+        atexit(destroy_);
+#endif
     }
 } // namespace