2 files changed, 51 insertions, 0 deletions
diff --git a/src/quick/items/qquicktextnodeengine.cpp b/src/quick/items/qquicktextnodeengine.cpp
index d6d31b4621..1be5e34e37 100644
--- a/src/quick/items/qquicktextnodeengine.cpp
+++ b/src/quick/items/qquicktextnodeengine.cpp
@@ -141,6 +141,8 @@ int QQuickTextNodeEngine::addText(const QTextBlock &block,
     while (textPos < fragmentEnd) {
         int blockRelativePosition = textPos - block.position();
         QTextLine line = block.layout()->lineForTextPosition(blockRelativePosition);
+        if (!line.isValid())
+            break;
         if (!currentLine().isValid()
                 || line.lineNumber() != currentLine().lineNumber()) {
             setCurrentLine(line);
diff --git a/tests/auto/quick/qquicktextdocument/tst_qquicktextdocument.cpp b/tests/auto/quick/qquicktextdocument/tst_qquicktextdocument.cpp
index e8c9f09413..50576f5cf2 100644
--- a/tests/auto/quick/qquicktextdocument/tst_qquicktextdocument.cpp
+++ b/tests/auto/quick/qquicktextdocument/tst_qquicktextdocument.cpp
@@ -16,6 +16,7 @@
 #include <QtQml/QQmlComponent>
 #include <QtQml/QQmlEngine>
 #include <QtQml/QQmlFile>
+#include <QtQuickTest/QtQuickTest>
 #include <QtQuickTestUtils/private/qmlutils_p.h>
 #include <QtQuickTestUtils/private/viewtestutils_p.h>
 #ifdef Q_OS_UNIX
@@ -46,6 +47,8 @@ private slots:
     void loadErrorPermissionDenied();
     void overrideTextFormat_data();
     void overrideTextFormat();
+    void changeCharFormatInRange_data();
+    void changeCharFormatInRange();
     void independentDocumentsSameSource_data();
     void independentDocumentsSameSource();
 };
@@ -574,6 +577,52 @@ void tst_qquicktextdocument::overrideTextFormat() // QTBUG-120772
     QVERIFY(textPropValue.startsWith(expectedFinalPrefix));
 }
 
+void tst_qquicktextdocument::changeCharFormatInRange_data()
+{
+    QTest::addColumn<bool>("editBlock");
+
+    QTest::newRow("begin/end") << true;
+    QTest::newRow("no edit block") << false; // QTBUG-126886 : don't crash
+}
+
+void tst_qquicktextdocument::changeCharFormatInRange()
+{
+    QFETCH(bool, editBlock);
+    QQuickView window;
+    QVERIFY(QQuickTest::showView(window, testFileUrl("initialText.qml")));
+    QQuickTextEdit *textEdit = qobject_cast<QQuickTextEdit *>(window.rootObject());
+    QVERIFY(textEdit);
+    QVERIFY(textEdit->textDocument());
+    auto *doc = textEdit->textDocument()->textDocument();
+    QVERIFY(doc);
+
+    QSignalSpy contentSpy(doc, &QTextDocument::contentsChanged);
+    const auto data = QStringLiteral("Format String");
+    doc->setPlainText(data);
+    auto block = doc->findBlockByNumber(0);
+
+    auto formatText = [block, data] {
+         QTextLayout::FormatRange formatText;
+         formatText.start = 0;
+         formatText.length = data.size();
+         formatText.format.setForeground(Qt::green);
+         block.layout()->setFormats({formatText});
+    };
+
+    // change the char format of this block, and verify visual effect
+    if (editBlock) {
+        QTextCursor cursor(doc);
+        cursor.beginEditBlock();
+        formatText();
+        cursor.endEditBlock();
+    } else {
+        formatText();
+    }
+
+    QVERIFY(QQuickTest::qWaitForPolish(textEdit));
+    QCOMPARE(contentSpy.size(), editBlock ? 2 : 1);
+}
+
 void tst_qquicktextdocument::independentDocumentsSameSource_data()
 {
     QTest::addColumn<QUrl>("qmlfile");