diff --git a/src/gui/text/qtextformat.cpp b/src/gui/text/qtextformat.cpp
index 10b8ade117..e94fad8890 100644
--- a/src/gui/text/qtextformat.cpp
+++ b/src/gui/text/qtextformat.cpp
@@ -201,10 +201,9 @@ public:
     inline void insertProperty(qint32 key, const QVariant &value)
     {
         hashDirty = true;
-        if ((key >= QTextFormat::FirstFontProperty && key <= QTextFormat::LastFontProperty)
-                || key == QTextFormat::FontLetterSpacingType) {
+        if (key >= QTextFormat::FirstFontProperty && key <= QTextFormat::LastFontProperty)
             fontDirty = true;
-        }
+
         for (int i = 0; i < props.count(); ++i)
             if (props.at(i).key == key) {
                 props[i].value = value;
@@ -218,10 +217,8 @@ public:
         for (int i = 0; i < props.count(); ++i)
             if (props.at(i).key == key) {
                 hashDirty = true;
-                if ((key >= QTextFormat::FirstFontProperty && key <= QTextFormat::LastFontProperty)
-                        || key == QTextFormat::FontLetterSpacingType) {
+                if (key >= QTextFormat::FirstFontProperty && key <= QTextFormat::LastFontProperty)
                     fontDirty = true;
-                }
                 props.remove(i);
                 return;
             }
@@ -444,7 +441,22 @@ void QTextFormatPrivate::recalcFont() const
 #ifndef QT_NO_DATASTREAM
 Q_GUI_EXPORT QDataStream &operator<<(QDataStream &stream, const QTextFormat &fmt)
 {
-    stream << fmt.format_type << fmt.properties();
+    QMap<int, QVariant> properties = fmt.properties();
+    if (stream.version() < QDataStream::Qt_6_0) {
+        auto it = properties.find(QTextFormat::FontLetterSpacingType);
+        if (it != properties.end()) {
+            properties[QTextFormat::OldFontLetterSpacingType] = it.value();
+            properties.erase(it);
+        }
+
+        it = properties.find(QTextFormat::FontStretch);
+        if (it != properties.end()) {
+            properties[QTextFormat::OldFontStretch] = it.value();
+            properties.erase(it);
+        }
+    }
+
+    stream << fmt.format_type << properties;
     return stream;
 }
 
@@ -459,8 +471,14 @@ Q_GUI_EXPORT QDataStream &operator>>(QDataStream &stream, QTextFormat &fmt)
         fmt.d = new QTextFormatPrivate();
 
     for (QMap<qint32, QVariant>::ConstIterator it = properties.constBegin();
-         it != properties.constEnd(); ++it)
-        fmt.d->insertProperty(it.key(), it.value());
+         it != properties.constEnd(); ++it) {
+        qint32 key = it.key();
+        if (key == QTextFormat::OldFontLetterSpacingType)
+            key = QTextFormat::FontLetterSpacingType;
+        else if (key == QTextFormat::OldFontStretch)
+            key = QTextFormat::FontStretch;
+        fmt.d->insertProperty(key, it.value());
+    }
 
     return stream;
 }
@@ -620,6 +638,8 @@ Q_GUI_EXPORT QDataStream &operator>>(QDataStream &stream, QTextFormat &fmt)
     \value IsAnchor
     \value AnchorHref
     \value AnchorName
+    \omitvalue OldFontLetterSpacingType
+    \omitvalue OldFontStretch
     \value ObjectType
 
     List properties
diff --git a/src/gui/text/qtextformat.h b/src/gui/text/qtextformat.h
index 28da0fe344..b4db18289e 100644
--- a/src/gui/text/qtextformat.h
+++ b/src/gui/text/qtextformat.h
@@ -184,16 +184,16 @@ public:
         // character properties
         FirstFontProperty = 0x1FE0,
         FontCapitalization = FirstFontProperty,
-        FontLetterSpacingType = 0x2033,
         FontLetterSpacing = 0x1FE1,
         FontWordSpacing = 0x1FE2,
-        FontStretch = 0x2034,
         FontStyleHint = 0x1FE3,
         FontStyleStrategy = 0x1FE4,
         FontKerning = 0x1FE5,
         FontHintingPreference = 0x1FE6,
         FontFamilies = 0x1FE7,
         FontStyleName = 0x1FE8,
+        FontLetterSpacingType = 0x1FE9,
+        FontStretch = 0x1FEA,
         FontFamily = 0x2000,
         FontPointSize = 0x2001,
         FontSizeAdjustment = 0x2002,
@@ -207,7 +207,7 @@ public:
         FontPixelSize = 0x2009,
         LastFontProperty = FontPixelSize,
 
-        TextUnderlineColor = 0x2010,
+        TextUnderlineColor = 0x2020,
         TextVerticalAlignment = 0x2021,
         TextOutline = 0x2022,
         TextUnderlineStyle = 0x2023,
@@ -216,6 +216,12 @@ public:
         IsAnchor = 0x2030,
         AnchorHref = 0x2031,
         AnchorName = 0x2032,
+
+        // Included for backwards compatibility with old QDataStreams.
+        // Should not be referenced in user code.
+        OldFontLetterSpacingType = 0x2033,
+        OldFontStretch = 0x2034,
+
         ObjectType = 0x2f00,
 
         // list properties
diff --git a/tests/auto/gui/text/qtextformat/tst_qtextformat.cpp b/tests/auto/gui/text/qtextformat/tst_qtextformat.cpp
index 4ab80bdcfe..4e5ef7c555 100644
--- a/tests/auto/gui/text/qtextformat/tst_qtextformat.cpp
+++ b/tests/auto/gui/text/qtextformat/tst_qtextformat.cpp
@@ -40,6 +40,10 @@
 #include <qtextlayout.h>
 #include <qabstracttextdocumentlayout.h>
 
+#ifndef QT_NO_DATASTREAM
+#  include <qdatastream.h>
+#endif
+
 class tst_QTextFormat : public QObject
 {
 Q_OBJECT
@@ -61,6 +65,10 @@ private slots:
     void setFont_collection_data();
     void setFont_collection();
     void clearCollection();
+
+#ifndef QT_NO_DATASTREAM
+    void dataStreamCompatibility();
+#endif
 };
 
 /*! \internal
@@ -677,5 +685,125 @@ void tst_QTextFormat::clearCollection()
     QCOMPARE(collection.defaultFont(), f); // kept, QTextDocument::clear or setPlainText should not reset the font set by setDefaultFont
 }
 
+#ifndef QT_NO_DATASTREAM
+void tst_QTextFormat::dataStreamCompatibility()
+{
+    // Make sure that we are still compatible with the old values of QTextFormat::FontLetterSpacingType
+    // and QTextFormat::FontStretch, when used with earlier QDataStream versions
+    QTextCharFormat format;
+    format.setFontStretch(42);
+    format.setFontLetterSpacingType(QFont::AbsoluteSpacing);
+
+    // Sanity check
+    {
+        QMap<int, QVariant> properties = format.properties();
+        QVERIFY(properties.contains(QTextFormat::FontLetterSpacingType));
+        QVERIFY(properties.contains(QTextFormat::FontStretch));
+        QVERIFY(!properties.contains(QTextFormat::OldFontLetterSpacingType));
+        QVERIFY(!properties.contains(QTextFormat::OldFontStretch));
+    }
+
+    QByteArray memory;
+
+    // Current stream version
+    {
+        {
+            QBuffer buffer(&memory);
+            buffer.open(QIODevice::WriteOnly);
+
+            QDataStream stream(&buffer);
+            stream << format;
+        }
+
+        {
+            QBuffer buffer(&memory);
+            buffer.open(QIODevice::ReadOnly);
+
+            QDataStream stream(&buffer);
+
+            QTextFormat other;
+            stream >> other;
+
+            {
+                QMap<int, QVariant> properties = other.properties();
+                QVERIFY(properties.contains(QTextFormat::FontLetterSpacingType));
+                QVERIFY(properties.contains(QTextFormat::FontStretch));
+                QVERIFY(!properties.contains(QTextFormat::OldFontLetterSpacingType));
+                QVERIFY(!properties.contains(QTextFormat::OldFontStretch));
+            }
+        }
+
+        {
+            QBuffer buffer(&memory);
+            buffer.open(QIODevice::ReadOnly);
+
+            QDataStream stream(&buffer);
+
+            quint32 type;
+            stream >> type;
+
+            QMap<qint32, QVariant> properties;
+            stream >> properties;
+            QVERIFY(properties.contains(QTextFormat::FontLetterSpacingType));
+            QVERIFY(properties.contains(QTextFormat::FontStretch));
+            QVERIFY(!properties.contains(QTextFormat::OldFontLetterSpacingType));
+            QVERIFY(!properties.contains(QTextFormat::OldFontStretch));
+        }
+    }
+
+    // Qt 5.15 stream version
+    memory.clear();
+    {
+        {
+            QBuffer buffer(&memory);
+            buffer.open(QIODevice::WriteOnly);
+
+            QDataStream stream(&buffer);
+            stream.setVersion(QDataStream::Qt_5_15);
+            stream << format;
+        }
+
+        {
+            QBuffer buffer(&memory);
+            buffer.open(QIODevice::ReadOnly);
+
+            QDataStream stream(&buffer);
+            stream.setVersion(QDataStream::Qt_5_15);
+
+            QTextFormat other;
+            stream >> other;
+
+            {
+                QMap<int, QVariant> properties = other.properties();
+                QVERIFY(properties.contains(QTextFormat::FontLetterSpacingType));
+                QVERIFY(properties.contains(QTextFormat::FontStretch));
+                QVERIFY(!properties.contains(QTextFormat::OldFontLetterSpacingType));
+                QVERIFY(!properties.contains(QTextFormat::OldFontStretch));
+            }
+        }
+
+        {
+            QBuffer buffer(&memory);
+            buffer.open(QIODevice::ReadOnly);
+
+            QDataStream stream(&buffer);
+            stream.setVersion(QDataStream::Qt_5_15);
+
+            quint32 type;
+            stream >> type;
+
+            // Verify that old data stream still has the compatibility values
+            QMap<qint32, QVariant> properties;
+            stream >> properties;
+            QVERIFY(!properties.contains(QTextFormat::FontLetterSpacingType));
+            QVERIFY(!properties.contains(QTextFormat::FontStretch));
+            QVERIFY(properties.contains(QTextFormat::OldFontLetterSpacingType));
+            QVERIFY(properties.contains(QTextFormat::OldFontStretch));
+        }
+    }
+
+}
+#endif // QT_NO_DATASTREAM
+
 QTEST_MAIN(tst_QTextFormat)
 #include "tst_qtextformat.moc"