diff --git a/src/widgets/widgets/qplaintextedit.cpp b/src/widgets/widgets/qplaintextedit.cpp
index bd7f844eca..8f0fff3d5c 100644
--- a/src/widgets/widgets/qplaintextedit.cpp
+++ b/src/widgets/widgets/qplaintextedit.cpp
@@ -289,7 +289,7 @@ void QPlainTextDocumentLayout::documentChanged(int from, int charsRemoved, int c
     Q_D(QPlainTextDocumentLayout);
     QTextDocument *doc = document();
     int newBlockCount = doc->blockCount();
-    int charsChanged = qMax(charsRemoved, charsAdded);
+    int charsChanged = charsRemoved + charsAdded;
 
     QTextBlock changeStartBlock = doc->findBlock(from);
     QTextBlock changeEndBlock = doc->findBlock(qMax(0, from + charsChanged - 1));
diff --git a/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp b/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp
index c47f7b1ff6..613d4fa28c 100644
--- a/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp
+++ b/tests/auto/widgets/widgets/qplaintextedit/tst_qplaintextedit.cpp
@@ -155,6 +155,7 @@ private slots:
     void findWithRegExpReturnsFalseIfNoMoreResults();
 #endif
     void layoutAfterMultiLineRemove();
+    void undoCommandRemovesAndReinsertsBlock();
 
 private:
     void createSelection();
@@ -1612,5 +1613,29 @@ void tst_QPlainTextEdit::layoutAfterMultiLineRemove()
     QCOMPARE(curs.blockNumber(), 3);
 }
 
+void tst_QPlainTextEdit::undoCommandRemovesAndReinsertsBlock()
+{
+    ed->setVisible(true);
+    ed->setPlainText(QStringLiteral("line1\nline2"));
+    QCOMPARE(ed->document()->blockCount(), 2);
+
+    QTextCursor cursor = ed->textCursor();
+    cursor.movePosition(QTextCursor::Start);
+    cursor.movePosition(QTextCursor::NextBlock, QTextCursor::KeepAnchor);
+    cursor.insertText(QStringLiteral("\n"));
+    QCOMPARE(ed->document()->blockCount(), 2);
+
+    ed->undo();
+    QCOMPARE(ed->document()->blockCount(), 2);
+
+    QTextBlock block;
+    for (block = ed->document()->begin(); block != ed->document()->end(); block = block.next()) {
+        QVERIFY(block.isValid());
+        QCOMPARE(block.length(), 6);
+        QVERIFY(block.layout()->lineForTextPosition(0).isValid());
+    }
+
+}
+
 QTEST_MAIN(tst_QPlainTextEdit)
 #include "tst_qplaintextedit.moc"