diff --git a/stl/inc/xlocnum b/stl/inc/xlocnum
index a14c070a63..1bc6413b0d 100644
--- a/stl/inc/xlocnum
+++ b/stl/inc/xlocnum
@@ -1376,7 +1376,7 @@ protected:
         const auto _Ngen = static_cast<size_t>(_CSTD sprintf_s(
             &_Buf[0], _Buf.size(), _Ffmt(_Fmt, 0, _Iosbase.flags()), static_cast<int>(_Precision), _Val));
 
-        return _Fput_v2(_Dest, _Iosbase, _Fill, _Buf.c_str(), _Ngen, (_STD isnan)(_Val));
+        return _Fput_v3(_Dest, _Iosbase, _Fill, _Buf.c_str(), _Ngen, (_STD isfinite)(_Val));
     }
 
     virtual _OutIt __CLR_OR_THIS_CALL do_put(
@@ -1400,7 +1400,7 @@ protected:
         const auto _Ngen = static_cast<size_t>(_CSTD sprintf_s(
             &_Buf[0], _Buf.size(), _Ffmt(_Fmt, 'L', _Iosbase.flags()), static_cast<int>(_Precision), _Val));
 
-        return _Fput_v2(_Dest, _Iosbase, _Fill, _Buf.c_str(), _Ngen, (_STD isnan)(_Val));
+        return _Fput_v3(_Dest, _Iosbase, _Fill, _Buf.c_str(), _Ngen, (_STD isfinite)(_Val));
     }
 #pragma warning(pop)
 
@@ -1463,12 +1463,12 @@ private:
 
     _OutIt __CLRCALL_OR_CDECL _Fput(_OutIt _Dest, ios_base& _Iosbase, _Elem _Fill, const char* _Buf,
         size_t _Count) const { // TRANSITION, ABI: preserved for binary compatibility
-        return _Fput_v2(_Dest, _Iosbase, _Fill, _Buf, _Count, false);
+        return _Fput_v3(_Dest, _Iosbase, _Fill, _Buf, _Count, true);
     }
 
     template <int = 0> // TRANSITION, ABI
-    _OutIt _Fput_v2(_OutIt _Dest, ios_base& _Iosbase, _Elem _Fill, const char* _Buf, size_t _Count,
-        bool _Is_nan_val) const { // put formatted floating-point to _Dest
+    _OutIt _Fput_v3(_OutIt _Dest, ios_base& _Iosbase, _Elem _Fill, const char* _Buf, size_t _Count,
+        bool _Is_finite_val) const { // put formatted floating-point to _Dest
         auto _Prefix = static_cast<size_t>(0 < _Count && (*_Buf == '+' || *_Buf == '-'));
         const char* _Exps;
         if ((_Iosbase.flags() & ios_base::floatfield) != ios_base::hexfloat) {
@@ -1497,7 +1497,7 @@ private:
             _Groupstring[_Poff] = _Punct_fac.decimal_point();
         }
 
-        if (!_Is_nan_val) {
+        if (_Is_finite_val) {
             size_t _Off     = _Poff == _Count ? _Eoff : _Poff;
             const char* _Pg = &_Grouping[0];
             while (*_Pg != CHAR_MAX && '\0' < *_Pg && static_cast<size_t>(*_Pg) < _Off - _Prefix) {
diff --git a/tests/libcxx/expected_results.txt b/tests/libcxx/expected_results.txt
index 224f1ffeca..7b912c8a6b 100644
--- a/tests/libcxx/expected_results.txt
+++ b/tests/libcxx/expected_results.txt
@@ -775,7 +775,6 @@ std/localization/locale.categories/category.monetary/locale.money.put/locale.mon
 std/localization/locale.categories/category.monetary/locale.money.put/locale.money.put.members/put_string_en_US.pass.cpp FAIL
 std/localization/locale.categories/category.monetary/locale.moneypunct/locale.moneypunct.members/decimal_point.pass.cpp FAIL
 std/localization/locale.categories/category.monetary/locale.moneypunct/locale.moneypunct.members/thousands_sep.pass.cpp FAIL
-std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_long_double.pass.cpp FAIL
 std/localization/locale.categories/category.time/locale.time.get/locale.time.get.members/get_monthname_wide.pass.cpp FAIL
 std/localization/locale.categories/category.time/locale.time.get/locale.time.get.members/get_monthname.pass.cpp FAIL
 std/localization/locale.categories/category.time/locale.time.get/locale.time.get.members/get_one.pass.cpp FAIL
diff --git a/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp b/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
index c7ac08d39e..73659075e5 100644
--- a/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
+++ b/tests/std/tests/Dev11_0496153_locale_ctor/test.cpp
@@ -10,16 +10,23 @@
 
 using namespace std;
 
-// The following monstrosity avoids activating the test code for _DLL compiles
-// that use a non-default value of _ITERATOR_DEBUG_LEVEL (_ITERATOR_DEBUG_LEVEL
-// defaults to "0" for release builds and "2" for _DEBUG).
-#if defined(_DLL) && (_ITERATOR_DEBUG_LEVEL == 1 || (defined(_DEBUG) != (_ITERATOR_DEBUG_LEVEL == 2)))
-#define ENABLE_TEST 0
+// Because std::string crosses the DLL boundary via overridden virtual functions,
+// we can test custom facets only when:
+// * linking statically, or
+// * linking dynamically with IDL set to its default value (so the user code and the DLL match).
+#ifdef _DEBUG
+#define DEFAULT_IDL 2
 #else
-#define ENABLE_TEST 1
-#endif // defined(_DLL) && (_ITERATOR_DEBUG_LEVEL == 1 || (defined(_DEBUG) != (_ITERATOR_DEBUG_LEVEL == 2)))
+#define DEFAULT_IDL 0
+#endif
 
-#if ENABLE_TEST
+#if !defined(_DLL) || _ITERATOR_DEBUG_LEVEL == DEFAULT_IDL
+#define TEST_CUSTOM_FACET 1
+#else
+#define TEST_CUSTOM_FACET 0
+#endif
+
+#if TEST_CUSTOM_FACET
 void test_Dev11_496153_locale_ctor_should_not_throw() noexcept {
     const locale loc(setlocale(LC_ALL, nullptr));
 
@@ -39,11 +46,11 @@ void test_VSO_159700_locale_should_support_user_defined_facets() {
     str << 1.5f;
     assert("locale didn't support user-defined facets" && str.str() == "1,5");
 }
-#endif // ENABLE_TEST
+#endif // TEST_CUSTOM_FACET
 
 int main() {
-#if ENABLE_TEST
+#if TEST_CUSTOM_FACET
     test_Dev11_496153_locale_ctor_should_not_throw();
     test_VSO_159700_locale_should_support_user_defined_facets();
-#endif // ENABLE_TEST
+#endif // TEST_CUSTOM_FACET
 }
diff --git a/tests/std/tests/GH_003867_output_nan/test.cpp b/tests/std/tests/GH_003867_output_nan/test.cpp
index a0c56d286a..e36c6779fc 100644
--- a/tests/std/tests/GH_003867_output_nan/test.cpp
+++ b/tests/std/tests/GH_003867_output_nan/test.cpp
@@ -5,16 +5,53 @@
 #include <limits>
 #include <locale>
 #include <sstream>
+#include <string>
 
 using namespace std;
 
+// Because std::string crosses the DLL boundary via overridden virtual functions,
+// we can test custom facets only when:
+// * linking statically, or
+// * linking dynamically with IDL set to its default value (so the user code and the DLL match).
+#ifdef _DEBUG
+#define DEFAULT_IDL 2
+#else
+#define DEFAULT_IDL 0
+#endif
+
+#if !defined(_DLL) || _ITERATOR_DEBUG_LEVEL == DEFAULT_IDL
+#define TEST_CUSTOM_FACET 1
+#else
+#define TEST_CUSTOM_FACET 0
+#endif
+
+#if TEST_CUSTOM_FACET
+struct groups_of_1 : numpunct<char> {
+    // The standard char specialization of std::numpunct::do_thousands_sep returns ','
+    string do_grouping() const override {
+        return "\1";
+    } // groups of 1 digit
+};
+#endif // TEST_CUSTOM_FACET
+
 template <typename T>
 void test_gh_3867() {
     // GH-3867 Writing NaN to the output stream with a set locale results in a weird output
-    ostringstream s;
-    s.imbue(locale("en-US"));
-    s << -numeric_limits<T>::quiet_NaN();
-    assert(s.str() == "-nan(ind)");
+    {
+        ostringstream s;
+        s.imbue(locale("en-US"));
+        s << -numeric_limits<T>::quiet_NaN();
+        assert(s.str() == "-nan(ind)");
+    }
+
+#if TEST_CUSTOM_FACET
+    {
+        ostringstream s;
+        s.imbue(locale(s.getloc(), new groups_of_1));
+        s << -numeric_limits<T>::infinity();
+        assert(s.str() == "-inf");
+    }
+#endif // TEST_CUSTOM_FACET
 }
 
 int main() {