diff --git a/stl/src/xfvalues.cpp b/stl/src/xfvalues.cpp
index 5822c050fae..d0329ee4860 100644
--- a/stl/src/xfvalues.cpp
+++ b/stl/src/xfvalues.cpp
@@ -28,6 +28,6 @@ extern /* const */ _Dconst _FNan    = {INIT((_FMAX << _FOFF) | (1 << (_FOFF - 1)
 extern /* const */ _Dconst _FSnan   = {INIT2(_FMAX << _FOFF, 1)};
 extern const _Dconst _FRteps        = {INIT((_FBIAS - NBITS / 2) << _FOFF)};
 
-extern const float _FXbig = (NBITS + 1) * 347L / 1000;
+extern const float _FXbig = (NBITS + 2) * 0.347f;
 
 _END_EXTERN_C_UNLESS_PURE
diff --git a/stl/src/xlvalues.cpp b/stl/src/xlvalues.cpp
index c2720fe8d16..7ec133738c2 100644
--- a/stl/src/xlvalues.cpp
+++ b/stl/src/xlvalues.cpp
@@ -26,4 +26,4 @@ extern /* const */ _Dconst _LNan    = {INIT((_DMAX << _DOFF) | (1 << (_DOFF - 1)
 extern /* const */ _Dconst _LSnan   = {INIT2(_DMAX << _DOFF, 1)};
 extern const _Dconst _LRteps        = {INIT((_DBIAS - NBITS / 2) << _DOFF)};
 
-extern const long double _LXbig = (NBITS + 1) * 347L / 1000;
+extern const long double _LXbig = (NBITS + 2) * 0.347L;
diff --git a/stl/src/xvalues.cpp b/stl/src/xvalues.cpp
index e48d493d42c..1d9a1fb1e30 100644
--- a/stl/src/xvalues.cpp
+++ b/stl/src/xvalues.cpp
@@ -28,4 +28,4 @@ extern /* const */ _Dconst _Nan     = {INIT((_DMAX << _DOFF) | (1 << (_DOFF - 1)
 extern /* const */ _Dconst _Snan    = {INIT2(_DMAX << _DOFF, 1)};
 extern const _Dconst _Rteps         = {INIT((_DBIAS - NBITS / 2) << _DOFF)};
 
-extern const double _Xbig = (NBITS + 1) * 347L / 1000;
+extern const double _Xbig = (NBITS + 2) * 0.347;
diff --git a/tests/std/test.lst b/tests/std/test.lst
index 0e60c21053b..34b48abda6f 100644
--- a/tests/std/test.lst
+++ b/tests/std/test.lst
@@ -164,6 +164,7 @@ tests\GH_000890_pow_template
 tests\GH_000940_missing_valarray_copy
 tests\GH_001010_filesystem_error_encoding
 tests\GH_001017_discrete_distribution_out_of_range
+tests\GH_001059_hyperbolic_truncation
 tests\GH_001086_partial_sort_copy
 tests\GH_001103_countl_zero_correctness
 tests\LWG2597_complex_branch_cut
diff --git a/tests/std/tests/GH_001059_hyperbolic_truncation/env.lst b/tests/std/tests/GH_001059_hyperbolic_truncation/env.lst
new file mode 100644
index 00000000000..19f025bd0e6
--- /dev/null
+++ b/tests/std/tests/GH_001059_hyperbolic_truncation/env.lst
@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_matrix.lst
diff --git a/tests/std/tests/GH_001059_hyperbolic_truncation/test.cpp b/tests/std/tests/GH_001059_hyperbolic_truncation/test.cpp
new file mode 100644
index 00000000000..67d69e1bb9a
--- /dev/null
+++ b/tests/std/tests/GH_001059_hyperbolic_truncation/test.cpp
@@ -0,0 +1,63 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// GH-1059: "Incorrect const float values in xvalues.cpp files"
+// The _Xbig constants, used to determine when the exp(-x) terms in
+// cosh and sinh can be ignored, have off-by-one and integer
+// truncation errors.
+
+#include <array>
+#include <cassert>
+#include <cmath>
+#include <complex>
+#include <iostream>
+#include <limits>
+
+using namespace std;
+
+template <class T>
+void Test(T x) {
+    const complex<T> z{x};
+    const T exp_over_2 = T{0.5} * real(exp(z));
+
+    const T cosh_expected = exp_over_2 + T{0.25} / exp_over_2;
+    const T cosh_calc     = real(cosh(z));
+    if (cosh_expected != cosh_calc) {
+        cout.precision(numeric_limits<T>::digits10 + 2);
+        cout << "x = " << x << '\n'
+             << "cosh (expected)   = " << cosh_expected << '\n'
+             << "cosh (calculated) = " << cosh_calc << endl;
+        assert(cosh_expected == cosh_calc);
+    }
+
+    const T sinh_expected = exp_over_2 - T{0.25} / exp_over_2;
+    const T sinh_calc     = real(sinh(z));
+    if (sinh_expected != sinh_calc) {
+        cout.precision(numeric_limits<T>::digits10 + 2);
+        cout << "x = " << x << '\n'
+             << "sinh (expected)   = " << sinh_expected << '\n'
+             << "sinh (calculated) = " << sinh_calc << endl;
+        assert(sinh_expected == sinh_calc);
+    }
+}
+
+template <class T>
+constexpr array<T, 3> GenerateValues() {
+    // {old crossover, difference ~ 1 ulp, difference ~ ulp/2}
+    constexpr int DIG = numeric_limits<T>::digits;
+    return {DIG * 347L / 1000L, DIG * static_cast<T>(0.347), (DIG + 1) * static_cast<T>(0.347)};
+}
+
+int main() {
+    constexpr auto fValues{GenerateValues<float>()};
+    for (const auto& x : fValues) {
+        Test<float>(x);
+    }
+
+    constexpr auto dValues{GenerateValues<double>()};
+    for (const auto& x : dValues) {
+        Test<double>(x);
+    }
+
+    return 0;
+}