diff --git a/src/corelib/global/qtenvironmentvariables.cpp b/src/corelib/global/qtenvironmentvariables.cpp
index ffafbdf4180..aab7e516d8e 100644
--- a/src/corelib/global/qtenvironmentvariables.cpp
+++ b/src/corelib/global/qtenvironmentvariables.cpp
@@ -174,6 +174,8 @@ bool qEnvironmentVariableIsEmpty(const char *varName) noexcept
 #endif
 }
 
+QT_WARNING_PUSH
+QT_WARNING_DISABLE_GCC("-Wmaybe-uninitialized") // older GCC don't like libstdc++'s std::optional
 /*!
     \relates <QtEnvironmentVariables>
     \since 5.5
@@ -195,11 +197,14 @@ bool qEnvironmentVariableIsEmpty(const char *varName) noexcept
 */
 int qEnvironmentVariableIntValue(const char *varName, bool *ok) noexcept
 {
-    std::optional<int> value = qEnvironmentVariableIntegerValue(varName);
+    std::optional<qint64> value = qEnvironmentVariableIntegerValue(varName);
+    if (value && *value != int(*value))
+        value = std::nullopt;
     if (ok)
         *ok = bool(value);
     return value.value_or(0);
 }
+QT_WARNING_POP
 
 /*!
     \relates <QtEnvironmentVariables>
@@ -232,11 +237,11 @@ int qEnvironmentVariableIntValue(const char *varName, bool *ok) noexcept
 
     \sa qgetenv(), qEnvironmentVariable(), qEnvironmentVariableIsSet()
 */
-std::optional<int> qEnvironmentVariableIntegerValue(const char *varName) noexcept
+std::optional<qint64> qEnvironmentVariableIntegerValue(const char *varName) noexcept
 {
     static const int NumBinaryDigitsPerOctalDigit = 3;
     static const int MaxDigitsForOctalInt =
-        (std::numeric_limits<uint>::digits + NumBinaryDigitsPerOctalDigit - 1) / NumBinaryDigitsPerOctalDigit
+        (std::numeric_limits<quint64>::digits + NumBinaryDigitsPerOctalDigit - 1) / NumBinaryDigitsPerOctalDigit
             + 1     // sign
             + 1;    // "0" base prefix
 
@@ -255,7 +260,7 @@ std::optional<int> qEnvironmentVariableIntegerValue(const char *varName) noexcep
         return std::nullopt;
 #endif
     auto r = QLocaleData::bytearrayToLongLong(QByteArrayView(buffer, size), 0);
-    if (!r.ok() || int(r.result) != r.result)
+    if (!r.ok())
         return std::nullopt;
     return r.result;
 }
diff --git a/src/corelib/global/qtenvironmentvariables.h b/src/corelib/global/qtenvironmentvariables.h
index 24658c415e5..9f650d35aff 100644
--- a/src/corelib/global/qtenvironmentvariables.h
+++ b/src/corelib/global/qtenvironmentvariables.h
@@ -7,6 +7,7 @@
 #include <QtCore/qtconfigmacros.h>
 #include <QtCore/qtcoreexports.h>
 #include <QtCore/qtdeprecationmarkers.h>
+#include <QtCore/qtypes.h>
 
 #include <optional>
 
@@ -34,7 +35,7 @@ Q_CORE_EXPORT bool qunsetenv(const char *varName);
 Q_CORE_EXPORT bool qEnvironmentVariableIsEmpty(const char *varName) noexcept;
 Q_CORE_EXPORT bool qEnvironmentVariableIsSet(const char *varName) noexcept;
 Q_CORE_EXPORT int  qEnvironmentVariableIntValue(const char *varName, bool *ok=nullptr) noexcept;
-Q_CORE_EXPORT std::optional<int> qEnvironmentVariableIntegerValue(const char *varName) noexcept;
+Q_CORE_EXPORT std::optional<qint64> qEnvironmentVariableIntegerValue(const char *varName) noexcept;
 
 QT_END_NAMESPACE
 
diff --git a/src/gui/kernel/qhighdpiscaling.cpp b/src/gui/kernel/qhighdpiscaling.cpp
index 9e38353e419..7bc2e0bc673 100644
--- a/src/gui/kernel/qhighdpiscaling.cpp
+++ b/src/gui/kernel/qhighdpiscaling.cpp
@@ -394,7 +394,7 @@ void QHighDpiScaling::initHighDpiScaling()
 
     // Read environment variables
     static const char* envDebugStr = "environment variable set:";
-    std::optional<int> envEnableHighDpiScaling = qEnvironmentVariableIntegerValue(enableHighDpiScalingEnvVar);
+    std::optional envEnableHighDpiScaling = qEnvironmentVariableIntegerValue(enableHighDpiScalingEnvVar);
     if (envEnableHighDpiScaling.has_value())
         qCDebug(lcHighDpi) << envDebugStr << enableHighDpiScalingEnvVar << envEnableHighDpiScaling.value();
 
@@ -406,7 +406,7 @@ void QHighDpiScaling::initHighDpiScaling()
     if (envScreenFactors.has_value())
         qCDebug(lcHighDpi) << envDebugStr << screenFactorsEnvVar << envScreenFactors.value();
 
-    std::optional<int> envUsePhysicalDpi = qEnvironmentVariableIntegerValue(usePhysicalDpiEnvVar);
+    std::optional envUsePhysicalDpi = qEnvironmentVariableIntegerValue(usePhysicalDpiEnvVar);
     if (envUsePhysicalDpi.has_value())
         qCDebug(lcHighDpi) << envDebugStr << usePhysicalDpiEnvVar << envUsePhysicalDpi.value();
 
diff --git a/tests/auto/corelib/global/qgetputenv/tst_qgetputenv.cpp b/tests/auto/corelib/global/qgetputenv/tst_qgetputenv.cpp
index 01be9463813..c932fe85706 100644
--- a/tests/auto/corelib/global/qgetputenv/tst_qgetputenv.cpp
+++ b/tests/auto/corelib/global/qgetputenv/tst_qgetputenv.cpp
@@ -6,6 +6,9 @@
 #include <QTest>
 
 #include <qglobal.h>
+
+#include <q20utility.h>
+
 #ifdef Q_OS_WIN
 #include <qt_windows.h>
 #endif
@@ -136,17 +139,17 @@ void tst_QGetPutEnv::encoding()
 void tst_QGetPutEnv::intValue_data()
 {
     QTest::addColumn<QByteArray>("value");
-    QTest::addColumn<int>("expected");
+    QTest::addColumn<qint64>("expected");
     QTest::addColumn<bool>("ok");
 
     // some repetition from what is tested in getSetCheck()
-    QTest::newRow("empty") << QByteArray() << 0 << false;
-    QTest::newRow("spaces-heading") << QByteArray(" \n\r\t1") << 1 << true;
-    QTest::newRow("spaces-trailing") << QByteArray("1 \n\r\t") << 1 << true;
-    QTest::newRow("junk-heading") << QByteArray("x1") << 0 << false;
-    QTest::newRow("junk-trailing") << QByteArray("1x") << 0 << false;
+    QTest::newRow("empty") << QByteArray() << qint64(0) << false;
+    QTest::newRow("spaces-heading") << QByteArray(" \n\r\t1") << qint64(1) << true;
+    QTest::newRow("spaces-trailing") << QByteArray("1 \n\r\t") << qint64(1) << true;
+    QTest::newRow("junk-heading") << QByteArray("x1") << qint64(0) << false;
+    QTest::newRow("junk-trailing") << QByteArray("1x") << qint64(0) << false;
 
-    auto addRow = [](const char *text, int expected, bool ok) {
+    auto addRow = [](const char *text, qint64 expected, bool ok) {
         QTest::newRow(text) << QByteArray(text) << expected << ok;
     };
     addRow("auto", 0, false);
@@ -168,10 +171,8 @@ void tst_QGetPutEnv::intValue_data()
     addRow("-1", -1, true);
     addRow("-010", -8, true);
     addRow("-000000000000000000000000000000000000000000000000001", 0, false);
-    // addRow("0xffffffff", -1, true); // could be expected, but not how QByteArray::toInt() works
-    addRow("0xffffffff", 0, false);
 
-    auto addNumWithBase = [](qlonglong num, int base) {
+    auto addNumWithBase = [](auto num, int base) {
         QByteArray text;
         {
             QTextStream s(&text);
@@ -179,42 +180,53 @@ void tst_QGetPutEnv::intValue_data()
             s << Qt::showbase << num;
         }
         QTestData &row = QTest::addRow("%s", text.constData()) << text;
-        if (num == int(num))
-            row << int(num) << true;
+        bool ok = true;
+        if constexpr (std::is_same_v<decltype(num), quint64>)
+            ok = num <= quint64(LLONG_MAX);
+        if (ok)
+            row << qint64(num) << true;
         else
-            row << 0 << false;
+            row << qint64(0) << false;
     };
     for (int base : {10, 8, 16}) {
         addNumWithBase(INT_MAX, base);
         addNumWithBase(qlonglong(INT_MAX) + 1, base);
+        addNumWithBase(UINT_MAX, base);
         addNumWithBase(INT_MIN, base);
         addNumWithBase(qlonglong(INT_MIN) - 1 , base);
+        addNumWithBase(LLONG_MAX, base);
+        addNumWithBase(LLONG_MIN, base);
+        addNumWithBase(ULLONG_MAX, base);
     };
 }
 
 void tst_QGetPutEnv::intValue()
 {
-    const int maxlen = (sizeof(int) * CHAR_BIT + 2) / 3;
+    const int maxlen = (sizeof(qint64) * CHAR_BIT + 2) / 3;
     const char varName[] = "should_not_exist";
 
     QFETCH(QByteArray, value);
-    QFETCH(int, expected);
+    QFETCH(qint64, expected);
     QFETCH(bool, ok);
 
     bool actualOk = !ok;
+    bool is32Bit = q20::in_range<int>(expected);
 
     // Self-test: confirm that it was like the docs said it should be
     if (value.size() < maxlen) {
-        QCOMPARE(value.toInt(&actualOk, 0), expected);
+        // 32-bit
+        QCOMPARE(value.toInt(&actualOk, 0), is32Bit ? expected : 0);
+        QCOMPARE(actualOk, ok && is32Bit);
+        QCOMPARE(value.toLongLong(&actualOk, 0), expected);
         QCOMPARE(actualOk, ok);
     }
 
     actualOk = !ok;
     QVERIFY(qputenv(varName, value));
-    QCOMPARE(qEnvironmentVariableIntValue(varName), expected);
-    QCOMPARE(qEnvironmentVariableIntValue(varName, &actualOk), expected);
-    QCOMPARE(actualOk, ok);
-    if (actualOk)
+    QCOMPARE(qEnvironmentVariableIntValue(varName), is32Bit ? expected : 0);
+    QCOMPARE(qEnvironmentVariableIntValue(varName, &actualOk), is32Bit ? expected : 0);
+    QCOMPARE(actualOk, ok && is32Bit);
+    if (ok)
         QCOMPARE(qEnvironmentVariableIntegerValue(varName), expected);
     else
         QCOMPARE(qEnvironmentVariableIntegerValue(varName), std::nullopt);