diff --git a/src/corelib/io/qdebug.cpp b/src/corelib/io/qdebug.cpp
index d5bdfadba92..598355e4296 100644
--- a/src/corelib/io/qdebug.cpp
+++ b/src/corelib/io/qdebug.cpp
@@ -1329,9 +1329,19 @@ QDebugStateSaver::~QDebugStateSaver()
 */
 void qt_QMetaEnum_flagDebugOperator(QDebug &debug, size_t sizeofT, uint value)
 {
-    qt_QMetaEnum_flagDebugOperator<uint>(debug, sizeofT, value);
+    qt_QMetaEnum_flagDebugOperator(debug, sizeofT, quint64(value));
 }
 
+/*!
+    \internal
+    Ditto, for 64-bit.
+*/
+void qt_QMetaEnum_flagDebugOperator(QDebug &debug, size_t sizeofT, quint64 value)
+{
+    qt_QMetaEnum_flagDebugOperator<quint64>(debug, sizeofT, value);
+}
+
+
 #ifndef QT_NO_QOBJECT
 /*!
     \internal
@@ -1449,7 +1459,7 @@ QDebug qt_QMetaEnum_flagDebugOperator(QDebug &debug, quint64 value, const QMetaO
         debug << '(';
     }
 
-    debug << me.valueToKeys(static_cast<int>(value));
+    debug << me.valueToKeys(value);
 
     if (enumScope)
         debug << ')';
diff --git a/src/corelib/io/qdebug.h b/src/corelib/io/qdebug.h
index 9b86c8eb1a1..c4be5955c8e 100644
--- a/src/corelib/io/qdebug.h
+++ b/src/corelib/io/qdebug.h
@@ -526,6 +526,7 @@ inline QDebug operator<<(QDebug debug, const QTaggedPointer<T, Tag> &ptr)
 Q_CORE_EXPORT QDebug qt_QMetaEnum_debugOperator(QDebug&, qint64 value, const QMetaObject *meta, const char *name);
 Q_CORE_EXPORT QDebug qt_QMetaEnum_flagDebugOperator(QDebug &dbg, quint64 value, const QMetaObject *meta, const char *name);
 Q_CORE_EXPORT void qt_QMetaEnum_flagDebugOperator(QDebug &debug, size_t sizeofT, uint value);
+Q_CORE_EXPORT void qt_QMetaEnum_flagDebugOperator(QDebug &debug, size_t sizeofT, quint64 value);
 
 template <typename Int>
 void qt_QMetaEnum_flagDebugOperator(QDebug &debug, size_t sizeofT, Int value)
@@ -556,9 +557,13 @@ inline QDebug operator<<(QDebug debug, Flags flags)
     using UInt = typename QIntegerForSizeof<T>::Unsigned;
 #if !defined(QT_NO_QOBJECT)
     if constexpr (QtPrivate::IsQEnumHelper<T>::Value || QtPrivate::IsQEnumHelper<Flags>::Value) {
+        // if QFlags<T> is a Q_FLAG, we always zero-extend; if not, we need to
+        // allow it to sign-extend if it is signed (see QMetaEnum::valueToKeys)
+        using Int = std::conditional_t<QtPrivate::IsQEnumHelper<Flags>::Value, UInt,
+                                       std::underlying_type_t<T>>;
         const QMetaObject *obj = qt_getEnumMetaObject(T());
         const char *name = qt_getEnumName(T());
-        return qt_QMetaEnum_flagDebugOperator(debug, UInt(flags.toInt()), obj, name);
+        return qt_QMetaEnum_flagDebugOperator(debug, Int(flags.toInt()), obj, name);
     } else
 #endif
     {
diff --git a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
index 5d4d4048129..fafda8bce87 100644
--- a/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
+++ b/tests/auto/corelib/io/qdebug/tst_qdebug.cpp
@@ -54,9 +54,14 @@ class tst_QDebug: public QObject
 public:
     enum EnumType { EnumValue1 = 1, EnumValue2 = INT_MIN };
     enum FlagType { EnumFlag1 = 1, EnumFlag2 = INT_MIN };
+    enum Enum64Type { Enum64Value1 = 1, Enum64Value2 = Q_UINT64_C(0x1'0000'0002) };
+    enum Flag64Type : qlonglong { Enum64Flag1 = 1, Enum64Flag2 = Q_UINT64_C(0x1'0000'0002) };
     Q_ENUM(EnumType)
+    Q_ENUM(Enum64Type)
     Q_DECLARE_FLAGS(Flags, FlagType)
     Q_FLAG(Flags)
+    Q_DECLARE_FLAGS(Flags64, Flag64Type)
+    Q_FLAG(Flags64)
 
 private slots:
     void assignment() const;
@@ -88,6 +93,7 @@ private slots:
     void qDebugQByteArray() const;
     void qDebugQByteArrayView() const;
     void qDebugQFlags() const;
+    void qDebugQFlags64() const;
     void qDebugStdChrono_data() const;
     void qDebugStdChrono() const;
     void qDebugStdOptional() const;
@@ -106,6 +112,8 @@ private slots:
     void objcInObjcMode() const;
 #endif
 };
+Q_DECLARE_OPERATORS_FOR_FLAGS(tst_QDebug::Flags)
+Q_DECLARE_OPERATORS_FOR_FLAGS(tst_QDebug::Flags64)
 
 void tst_QDebug::assignment() const
 {
@@ -1096,8 +1104,9 @@ void tst_QDebug::qDebugQFlags() const
     QString file, function;
     int line = 0;
     QFlags<TestEnum> flags(Flag1 | Flag2 | SignFlag);
-
     MessageHandlerSetter mhs(myMessageHandler);
+
+    // first, test QFlags on an enum where neither are Q_FLAG or Q_ENUM
     { qDebug() << flags; }
 #ifndef QT_NO_MESSAGELOGCONTEXT
     file = __FILE__; line = __LINE__ - 2; function = Q_FUNC_INFO;
@@ -1108,17 +1117,54 @@ void tst_QDebug::qDebugQFlags() const
     QCOMPARE(s_line, line);
     QCOMPARE(QString::fromLatin1(s_function), function);
 
-    // Test the output of QFlags with an enum not declared with Q_DECLARE_FLAGS and Q_FLAGS
+    // QFlags where the backing enum is a Q_ENUM but the QFlags isn't a QFLAG
     QFlags<EnumType> flags2(EnumValue2);
     qDebug() << flags2;
     QCOMPARE(s_msg, QString::fromLatin1("QFlags<tst_QDebug::EnumType>(EnumValue2)"));
 
-    // A now for one that was fully declared
+    // And now for one that was fully declared
     tst_QDebug::Flags flags3(EnumFlag1);
     qDebug() << flags3;
     QCOMPARE(s_msg, QString::fromLatin1("QFlags<tst_QDebug::FlagType>(EnumFlag1)"));
 }
 
+enum class TestEnum64 : qulonglong {
+    Flag1 = 0x1,
+    Flag2 = Q_UINT64_C(0x8000'0000'0000'0000)
+};
+
+Q_DECLARE_FLAGS(TestFlags64, TestEnum64)
+Q_DECLARE_OPERATORS_FOR_FLAGS(TestFlags64)
+
+void tst_QDebug::qDebugQFlags64() const
+{
+    QString file, function;
+    int line = 0;
+    QFlags<TestEnum64> flags(TestEnum64::Flag1 | TestEnum64::Flag2);
+    MessageHandlerSetter mhs(myMessageHandler);
+
+    // first, test QFlags on an enum where neither are Q_FLAG or Q_ENUM
+    qDebug() << flags;
+#ifndef QT_NO_MESSAGELOGCONTEXT
+    file = __FILE__; line = __LINE__ - 2; function = Q_FUNC_INFO;
+#endif
+    QCOMPARE(s_msgType, QtDebugMsg);
+    QCOMPARE(s_msg, "QFlags(0x1|0x8000000000000000)");
+    QCOMPARE(QString::fromLatin1(s_file), file);
+    QCOMPARE(s_line, line);
+    QCOMPARE(QString::fromLatin1(s_function), function);
+
+    // QFlags where the backing enum is a Q_ENUM but the QFlags isn't a QFLAG
+    QFlags<Enum64Type> flags2(Enum64Value2);
+    qDebug() << flags2;
+    QCOMPARE(s_msg, QString::fromLatin1("QFlags<tst_QDebug::Enum64Type>(Enum64Value2)"));
+
+    // And now for one that was fully declared
+    tst_QDebug::Flags64 flags3(Enum64Flag1|Enum64Flag2);
+    qDebug() << flags3;
+    QCOMPARE(s_msg, QString::fromLatin1("QFlags<tst_QDebug::Flag64Type>(Enum64Flag1|Enum64Flag2)"));
+}
+
 using ToStringFunction = std::function<QString()>;
 void tst_QDebug::qDebugStdChrono_data() const
 {