diff --git a/stl/inc/xlocale b/stl/inc/xlocale
index 5a70bb2cb4..fb5d03cce7 100644
--- a/stl/inc/xlocale
+++ b/stl/inc/xlocale
@@ -144,7 +144,7 @@ public:
         _Atomic_counter_t _Myrefs; // the reference count
 
     protected:
-        explicit __CLR_OR_THIS_CALL facet(size_t _Initrefs = 0)
+        explicit __CLR_OR_THIS_CALL facet(size_t _Initrefs = 0) noexcept // strengthened
             : _Myrefs(static_cast<_Atomic_counter_t>(_Initrefs)) // non-atomic initialization
         {}
 
@@ -618,7 +618,9 @@ inline unsigned short* __CRTDECL _Maklocstr(const char* _Ptr, unsigned short*, c
 }
 #endif // defined(_NATIVE_WCHAR_T_DEFINED) && !_ENFORCE_FACET_SPECIALIZATIONS
 
-_EXPORT_STD extern "C++" class _CRTIMP2_PURE_IMPORT codecvt_base : public locale::facet { // base class for codecvt
+_EXPORT_STD extern "C++" class _CRTIMP2_PURE_IMPORT codecvt_base // base class for codecvt
+    : public locale::facet // TRANSITION, ABI, shouldn't be derived from locale::facet
+{
 public:
     enum { // constants for different parse states
         ok,
@@ -628,7 +630,8 @@ public:
     };
     using result = int;
 
-    __CLR_OR_THIS_CALL codecvt_base(size_t _Refs = 0) : locale::facet(_Refs) {}
+    __CLR_OR_THIS_CALL codecvt_base(size_t _Refs = 0) noexcept // strengthened
+        : locale::facet(_Refs) {}
 
     bool __CLR_OR_THIS_CALL always_noconv() const noexcept {
         // return true if conversions never change input (from codecvt)
@@ -2361,7 +2364,9 @@ protected:
 #define _UP _UPPER // 'A'-'Z'
 #define _XD _HEX // '0'-'9', 'A'-'F', 'a'-'f'
 
-_EXPORT_STD extern "C++" struct _CRTIMP2_PURE_IMPORT ctype_base : locale::facet { // base for ctype
+_EXPORT_STD extern "C++" struct _CRTIMP2_PURE_IMPORT ctype_base // base for ctype
+    : locale::facet // TRANSITION, ABI, shouldn't be derived from locale::facet
+{
     enum { // constants for character classifications
         alnum  = _DI | _LO | _UP | _XA,
         alpha  = _LO | _UP | _XA,
@@ -2378,7 +2383,8 @@ _EXPORT_STD extern "C++" struct _CRTIMP2_PURE_IMPORT ctype_base : locale::facet
     };
     using mask = short; // to match <ctype.h>
 
-    __CLR_OR_THIS_CALL ctype_base(size_t _Refs = 0) : locale::facet(_Refs) {}
+    __CLR_OR_THIS_CALL ctype_base(size_t _Refs = 0) noexcept // strengthened
+        : locale::facet(_Refs) {}
 
     __CLR_OR_THIS_CALL ~ctype_base() noexcept override {}
 };
diff --git a/stl/inc/xlocmes b/stl/inc/xlocmes
index 171bea273f..ca9355f1d9 100644
--- a/stl/inc/xlocmes
+++ b/stl/inc/xlocmes
@@ -18,10 +18,14 @@ _STL_DISABLE_CLANG_WARNINGS
 #undef new
 
 _STD_BEGIN
-_EXPORT_STD struct messages_base : locale::facet { // base class for messages
+_EXPORT_STD struct messages_base // base class for messages
+    : locale::facet // TRANSITION, ABI, shouldn't be derived from locale::facet
+{
     using catalog = int;
 
-    explicit messages_base(size_t _Refs = 0) : locale::facet(_Refs) {}
+    messages_base() noexcept // strengthened
+        : messages_base(0) {}
+    explicit messages_base(size_t _Refs) noexcept : locale::facet(_Refs) {}
 };
 
 _EXPORT_STD template <class _Elem>
diff --git a/stl/inc/xlocmon b/stl/inc/xlocmon
index a8c1eafabd..7fb534b852 100644
--- a/stl/inc/xlocmon
+++ b/stl/inc/xlocmon
@@ -19,7 +19,9 @@ _STL_DISABLE_CLANG_WARNINGS
 #undef new
 
 _STD_BEGIN
-_EXPORT_STD struct money_base : locale::facet { // ultimate base class for moneypunct
+_EXPORT_STD struct money_base // ultimate base class for moneypunct
+    : locale::facet // TRANSITION, ABI, shouldn't be derived from locale::facet
+{
     enum { // constants for different format codes
         symbol = '$',
         sign   = '+',
@@ -33,7 +35,8 @@ _EXPORT_STD struct money_base : locale::facet { // ultimate base class for money
         char field[4];
     };
 
-    money_base(size_t _Refs = 0) : locale::facet(_Refs) {}
+    money_base(size_t _Refs = 0) noexcept // strengthened
+        : locale::facet(_Refs) {}
 };
 
 template <class _Elem>
diff --git a/stl/inc/xloctime b/stl/inc/xloctime
index 722feeb330..8b30b8493e 100644
--- a/stl/inc/xloctime
+++ b/stl/inc/xloctime
@@ -86,7 +86,9 @@ ios_base::iostate _Getint_v2(_InIt& _First, _InIt& _Last, int _Lo, int _Hi, int&
     return _State;
 }
 
-_EXPORT_STD extern "C++" struct _CRTIMP2_PURE_IMPORT time_base : locale::facet { // base class for time_get
+_EXPORT_STD extern "C++" struct _CRTIMP2_PURE_IMPORT time_base // base class for time_get
+    : locale::facet // TRANSITION, ABI, shouldn't be derived from locale::facet
+{
     enum dateorder { // constants for different orders of date components
         no_order,
         dmy,
@@ -95,7 +97,8 @@ _EXPORT_STD extern "C++" struct _CRTIMP2_PURE_IMPORT time_base : locale::facet {
         ydm
     };
 
-    __CLR_OR_THIS_CALL time_base(size_t _Refs = 0) : locale::facet(_Refs) {}
+    __CLR_OR_THIS_CALL time_base(size_t _Refs = 0) noexcept // strengthened
+        : locale::facet(_Refs) {}
 
     __CLR_OR_THIS_CALL ~time_base() noexcept override {}
 };
diff --git a/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp b/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
index 7a7cd8f9bf..af6eacb8aa 100644
--- a/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
+++ b/tests/std/tests/Dev09_056375_locale_cleanup/test.cpp
@@ -14,6 +14,33 @@ using namespace std;
 STATIC_ASSERT(noexcept(locale{} == locale{}));
 STATIC_ASSERT(noexcept(locale{} != locale{}));
 
+STATIC_ASSERT(is_nothrow_default_constructible_v<ctype_base>); // strengthened
+STATIC_ASSERT(is_nothrow_default_constructible_v<codecvt_base>); // strengthened
+STATIC_ASSERT(is_nothrow_default_constructible_v<time_base>); // strengthened
+STATIC_ASSERT(is_nothrow_default_constructible_v<money_base>); // strengthened
+STATIC_ASSERT(is_nothrow_default_constructible_v<messages_base>); // strengthened
+
+// Test that *_base classes are implicitly default constructible.
+
+template <class T>
+void parameter_taker(const T&); // not defined
+
+template <class T, class = void>
+constexpr bool is_implicitly_default_constructible = false;
+
+template <class T>
+constexpr bool is_implicitly_default_constructible<T, void_t<decltype(parameter_taker<T>({}))>> = true;
+
+STATIC_ASSERT(is_implicitly_default_constructible<ctype_base>);
+STATIC_ASSERT(is_implicitly_default_constructible<codecvt_base>);
+STATIC_ASSERT(is_implicitly_default_constructible<time_base>);
+STATIC_ASSERT(is_implicitly_default_constructible<money_base>);
+STATIC_ASSERT(is_implicitly_default_constructible<messages_base>);
+
+STATIC_ASSERT(!is_implicitly_default_constructible<locale::facet>);
+STATIC_ASSERT(!is_implicitly_default_constructible<ctype<char>>);
+STATIC_ASSERT(!is_implicitly_default_constructible<ctype<wchar_t>>);
+
 void test_dll() {
     puts("Calling dll");
 #ifdef _M_CEE