diff --git a/stl/inc/xiosbase b/stl/inc/xiosbase
index 363a51c9575..a1b5ff24ae3 100644
--- a/stl/inc/xiosbase
+++ b/stl/inc/xiosbase
@@ -22,7 +22,6 @@ _STD_BEGIN
 template <class _Dummy>
 class _Iosb { // define templatized bitmask/enumerated types, instantiate on demand
 public:
-    enum _Dummy_enum { _Dummy_enum_val = 1 }; // don't ask, TRANSITION, ABI
     enum _Fmtflags { // constants for formatting options
         _Fmtmask = 0xffff,
         _Fmtzero = 0
@@ -46,10 +45,9 @@ public:
     static constexpr int hexfloat = 0x3000; // TRANSITION, ABI, GH-3296
 
     static constexpr int boolalpha   = 0x4000;
-    static constexpr int _Stdio      = 0x8000;
-    static constexpr int adjustfield = 0x01C0; // left | right | internal
-    static constexpr int basefield   = 0x0E00; // dec | oct | hex
-    static constexpr int floatfield  = 0x3000; // scientific | fixed
+    static constexpr int adjustfield = left | right | internal;
+    static constexpr int basefield   = dec | oct | hex;
+    static constexpr int floatfield  = scientific | fixed;
 
     enum _Iostate { // constants for stream states
         _Statmask = 0x17
@@ -60,10 +58,6 @@ public:
     static constexpr int failbit = 0x2;
     static constexpr int badbit  = 0x4;
 
-    enum _Openmode { // constants for file opening options
-        _Openmask = 0xff
-    };
-
     static constexpr int in         = 0x01;
     static constexpr int out        = 0x02;
     static constexpr int ate        = 0x04;
@@ -76,21 +70,18 @@ public:
     static constexpr int noreplace = _Noreplace;
 #endif
 
-    enum _Seekdir { // constants for file positioning options
-        _Seekbeg,
-        _Seekcur,
-        _Seekend
-    };
-
-    static constexpr int beg = _Seekbeg;
-    static constexpr int cur = _Seekcur;
-    static constexpr int end = _Seekend;
-
-    enum { // TRANSITION, ABI
-        _Openprot = _SH_DENYNO
-    };
+    static constexpr int beg = 0;
+    static constexpr int cur = 1;
+    static constexpr int end = 2;
 
     static constexpr int _Default_open_prot = _SH_DENYNO; // constant for default file opening protection
+
+    // TRANSITION, ABI: These enums don't appear in the STL DLL's export surface, but MaxMPDCompat
+    // in the MSVC-internal build detects that they appear in the CompatibilityData baseline.
+    enum _Dummy_enum { _Dummy_enum_val = 1 };
+    enum _Openmode { _Openmask = 0xff };
+    enum _Seekdir { _Seekbeg, _Seekcur, _Seekend };
+    enum { _Openprot = _SH_DENYNO };
 };
 
 _EXPORT_STD extern "C++" class _CRTIMP2_PURE_IMPORT ios_base : public _Iosb<int> { // base class for ios
diff --git a/stl/inc/xlocale b/stl/inc/xlocale
index d169357747f..0f3738223c6 100644
--- a/stl/inc/xlocale
+++ b/stl/inc/xlocale
@@ -23,34 +23,7 @@ _STL_DISABLE_CLANG_WARNINGS
 
 _STD_BEGIN
 template <class _Dummy>
-class _Locbase { // define templatized category constants, instantiate on demand
-public:
-    _PGLOBAL static const int collate  = _M_COLLATE;
-    _PGLOBAL static const int ctype    = _M_CTYPE;
-    _PGLOBAL static const int monetary = _M_MONETARY;
-    _PGLOBAL static const int numeric  = _M_NUMERIC;
-    _PGLOBAL static const int time     = _M_TIME;
-    _PGLOBAL static const int messages = _M_MESSAGES;
-    _PGLOBAL static const int all      = _M_ALL;
-    _PGLOBAL static const int none     = 0;
-};
-
-template <class _Dummy>
-const int _Locbase<_Dummy>::collate;
-template <class _Dummy>
-const int _Locbase<_Dummy>::ctype;
-template <class _Dummy>
-const int _Locbase<_Dummy>::monetary;
-template <class _Dummy>
-const int _Locbase<_Dummy>::numeric;
-template <class _Dummy>
-const int _Locbase<_Dummy>::time;
-template <class _Dummy>
-const int _Locbase<_Dummy>::messages;
-template <class _Dummy>
-const int _Locbase<_Dummy>::all;
-template <class _Dummy>
-const int _Locbase<_Dummy>::none;
+class _Locbase {}; // TRANSITION, ABI, affects sizeof(locale)
 
 _EXPORT_STD template <class _Elem>
 class collate;
@@ -90,6 +63,15 @@ _EXPORT_STD extern "C++" class locale : public _Locbase<int>, public _Crt_new_de
 public:
     using category = int;
 
+    static constexpr category collate  = _M_COLLATE;
+    static constexpr category ctype    = _M_CTYPE;
+    static constexpr category monetary = _M_MONETARY;
+    static constexpr category numeric  = _M_NUMERIC;
+    static constexpr category time     = _M_TIME;
+    static constexpr category messages = _M_MESSAGES;
+    static constexpr category all      = _M_ALL;
+    static constexpr category none     = 0;
+
     class _CRTIMP2_PURE_IMPORT id { // identifier stamp, unique for each distinct kind of facet
     public:
         __CLR_OR_THIS_CALL id(size_t _Val = 0) : _Id(_Val) {}