diff --git a/stl/inc/random b/stl/inc/random
index 1b558903ea9..eb3496e162a 100644
--- a/stl/inc/random
+++ b/stl/inc/random
@@ -70,7 +70,7 @@ _INLINE_VAR constexpr int _Nwords = 4;
 template <class _Elem, class _Traits>
 basic_ostream<_Elem, _Traits>& _Write(
     basic_ostream<_Elem, _Traits>& _Os, long double _Dx) { // write long double to stream
-    int _Ex;
+    int _Ex           = 0;
     long double _Frac = _CSTD frexpl(_Dx, &_Ex);
     for (int _Nw = 0; _Nw < _Nwords; ++_Nw) { // break into 31-bit words
         _Frac *= _Two31;
diff --git a/stl/inc/xlocnum b/stl/inc/xlocnum
index 29c3b8540ba..858ce353923 100644
--- a/stl/inc/xlocnum
+++ b/stl/inc/xlocnum
@@ -1385,15 +1385,15 @@ protected:
         const streamsize _Precision = _Is_hex ? -1 : _Iosbase.precision(); // precision setting
         const int _Desired_precision =
             _Float_put_desired_precision<double>(_Precision, _Float_flags); // desired precision
-        size_t _Bufsize = static_cast<size_t>(_Desired_precision);
-        if (_Is_fixed && 1e10 < _CSTD fabs(_Val)) { // f or F format
-            int _Ptwo;
+        size_t _Bufsize       = static_cast<size_t>(_Desired_precision);
+        const bool _Is_finite = (_STD isfinite) (_Val);
+        if (_Is_fixed && _Is_finite && 1e10 < _CSTD fabs(_Val)) { // f or F format
+            int _Ptwo = 0;
             (void) _CSTD frexp(_Val, &_Ptwo);
             _Bufsize += _CSTD abs(_Ptwo) * 30103L / 100000L;
         }
 
         _Buf.resize(_Bufsize + 50); // add fudge factor
-        const bool _Is_finite      = (_STD isfinite) (_Val);
         const auto _Adjusted_flags = // TRANSITION, DevCom-10519861
             _Is_finite ? _Iosbase.flags() : _Iosbase.flags() & ~ios_base::showpoint;
 
@@ -1419,15 +1419,15 @@ protected:
         const streamsize _Precision = _Is_hex ? -1 : _Iosbase.precision(); // precision setting
         const int _Desired_precision =
             _Float_put_desired_precision<long double>(_Precision, _Float_flags); // desired precision
-        size_t _Bufsize = static_cast<size_t>(_Desired_precision);
-        if (_Is_fixed && 1e10 < _CSTD fabsl(_Val)) { // f or F format
-            int _Ptwo;
+        size_t _Bufsize       = static_cast<size_t>(_Desired_precision);
+        const bool _Is_finite = (_STD isfinite) (_Val);
+        if (_Is_fixed && _Is_finite && 1e10 < _CSTD fabsl(_Val)) { // f or F format
+            int _Ptwo = 0;
             (void) _CSTD frexpl(_Val, &_Ptwo);
             _Bufsize += _CSTD abs(_Ptwo) * 30103L / 100000L;
         }
 
         _Buf.resize(_Bufsize + 50); // add fudge factor
-        const bool _Is_finite      = (_STD isfinite) (_Val);
         const auto _Adjusted_flags = // TRANSITION, DevCom-10519861
             _Is_finite ? _Iosbase.flags() : _Iosbase.flags() & ~ios_base::showpoint;
 
diff --git a/tests/std/tests/GH_003867_output_nan/test.cpp b/tests/std/tests/GH_003867_output_nan/test.cpp
index 059ed13cca5..b25ed7cf176 100644
--- a/tests/std/tests/GH_003867_output_nan/test.cpp
+++ b/tests/std/tests/GH_003867_output_nan/test.cpp
@@ -58,7 +58,8 @@ void test_gh_3867() {
 // Also test GH-4210: With setprecision(0) showpoint fixed, a bogus '.' is emitted for infinity and NaN
 
 template <class FloatingPoint>
-void test_output_nonfinite_value(const FloatingPoint x) {
+void test_output_nonfinite_value(
+    const FloatingPoint x, const string& expected_noshowpos, const string& expected_showpos) {
     const auto s1 = [x] {
         ostringstream os;
         os << setprecision(0) << showpoint << fixed;
@@ -72,6 +73,7 @@ void test_output_nonfinite_value(const FloatingPoint x) {
         return os.str();
     }();
     assert(s1 == s2);
+    assert(s1 == expected_noshowpos);
 
     const auto s3 = [x] {
         ostringstream os;
@@ -86,6 +88,7 @@ void test_output_nonfinite_value(const FloatingPoint x) {
         return os.str();
     }();
     assert(s3 == s4);
+    assert(s3 == expected_showpos);
 }
 
 template <class FloatingPoint>
@@ -93,10 +96,11 @@ void test_gh_4210() {
     constexpr auto inf_val = numeric_limits<FloatingPoint>::infinity();
     constexpr auto nan_val = numeric_limits<FloatingPoint>::quiet_NaN();
 
-    test_output_nonfinite_value(inf_val);
-    test_output_nonfinite_value(-inf_val);
-    test_output_nonfinite_value(nan_val);
-    test_output_nonfinite_value(-nan_val);
+    // These expected results are implementation-defined:
+    test_output_nonfinite_value(inf_val, "inf", "+inf");
+    test_output_nonfinite_value(-inf_val, "-inf", "-inf");
+    test_output_nonfinite_value(nan_val, "nan", "+nan");
+    test_output_nonfinite_value(-nan_val, "-nan(ind)", "-nan(ind)");
 }
 
 int main() {