diff --git a/src/gui/text/qtextdocument.cpp b/src/gui/text/qtextdocument.cpp
index 3652a180a8..22c249d604 100644
--- a/src/gui/text/qtextdocument.cpp
+++ b/src/gui/text/qtextdocument.cpp
@@ -1970,9 +1970,12 @@ void QTextDocument::print(QPagedPaintDevice *printer) const
     QRectF body = QRectF(QPointF(0, 0), d->pageSize);
     QPointF pageNumberPos;
 
+    qreal sourceDpiX = qt_defaultDpiX();
+    qreal sourceDpiY = qt_defaultDpiY();
+    const qreal dpiScaleX = qreal(printer->logicalDpiX()) / sourceDpiX;
+    const qreal dpiScaleY = qreal(printer->logicalDpiY()) / sourceDpiY;
+
     if (documentPaginated) {
-        qreal sourceDpiX = qt_defaultDpi();
-        qreal sourceDpiY = sourceDpiX;
 
         QPaintDevice *dev = doc->documentLayout()->paintDevice();
         if (dev) {
@@ -1980,9 +1983,6 @@ void QTextDocument::print(QPagedPaintDevice *printer) const
             sourceDpiY = dev->logicalDpiY();
         }
 
-        const qreal dpiScaleX = qreal(printer->logicalDpiX()) / sourceDpiX;
-        const qreal dpiScaleY = qreal(printer->logicalDpiY()) / sourceDpiY;
-
         // scale to dpi
         p.scale(dpiScaleX, dpiScaleY);
 
@@ -2011,15 +2011,21 @@ void QTextDocument::print(QPagedPaintDevice *printer) const
         // copy the custom object handlers
         layout->d_func()->handlers = documentLayout()->d_func()->handlers;
 
-        int dpiy = p.device()->logicalDpiY();
-        int margin = (int) ((2/2.54)*dpiy); // 2 cm margins
+        // 2 cm margins, scaled to device in QTextDocumentLayoutPrivate::layoutFrame
+        const int horizontalMargin = int((2/2.54)*sourceDpiX);
+        const int verticalMargin = int((2/2.54)*sourceDpiY);
         QTextFrameFormat fmt = doc->rootFrame()->frameFormat();
-        fmt.setMargin(margin);
+        fmt.setLeftMargin(horizontalMargin);
+        fmt.setRightMargin(horizontalMargin);
+        fmt.setTopMargin(verticalMargin);
+        fmt.setBottomMargin(verticalMargin);
         doc->rootFrame()->setFrameFormat(fmt);
 
+        // pageNumberPos must be in device coordinates, so scale to device here
+        const int dpiy = p.device()->logicalDpiY();
         body = QRectF(0, 0, printer->width(), printer->height());
-        pageNumberPos = QPointF(body.width() - margin,
-                                body.height() - margin
+        pageNumberPos = QPointF(body.width() - horizontalMargin * dpiScaleX,
+                                body.height() - verticalMargin * dpiScaleY
                                 + QFontMetrics(doc->defaultFont(), p.device()).ascent()
                                 + 5 * dpiy / 72.0);
         clonedDoc->setPageSize(body.size());
diff --git a/src/gui/text/qtextdocumentlayout.cpp b/src/gui/text/qtextdocumentlayout.cpp
index b02723c047..a9a177da8b 100644
--- a/src/gui/text/qtextdocumentlayout.cpp
+++ b/src/gui/text/qtextdocumentlayout.cpp
@@ -2915,24 +2915,24 @@ QRectF QTextDocumentLayoutPrivate::layoutFrame(QTextFrame *f, int layoutFrom, in
     {
         QTextFrameFormat fformat = f->frameFormat();
         // set sizes of this frame from the format
-        QFixed tm = QFixed::fromReal(fformat.topMargin());
+        QFixed tm = QFixed::fromReal(scaleToDevice(fformat.topMargin())).round();
         if (tm != fd->topMargin) {
             fd->topMargin = tm;
             fullLayout = true;
         }
-        QFixed bm = QFixed::fromReal(fformat.bottomMargin());
+        QFixed bm = QFixed::fromReal(scaleToDevice(fformat.bottomMargin())).round();
         if (bm != fd->bottomMargin) {
             fd->bottomMargin = bm;
             fullLayout = true;
         }
-        fd->leftMargin = QFixed::fromReal(fformat.leftMargin());
-        fd->rightMargin = QFixed::fromReal(fformat.rightMargin());
-        QFixed b = QFixed::fromReal(fformat.border());
+        fd->leftMargin = QFixed::fromReal(scaleToDevice(fformat.leftMargin())).round();
+        fd->rightMargin = QFixed::fromReal(scaleToDevice(fformat.rightMargin())).round();
+        QFixed b = QFixed::fromReal(scaleToDevice(fformat.border())).round();
         if (b != fd->border) {
             fd->border = b;
             fullLayout = true;
         }
-        QFixed p = QFixed::fromReal(fformat.padding());
+        QFixed p = QFixed::fromReal(scaleToDevice(fformat.padding())).round();
         if (p != fd->padding) {
             fd->padding = p;
             fullLayout = true;
diff --git a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
index c2cf31bfa4..b31e230893 100644
--- a/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
+++ b/tests/auto/widgets/widgets/qtextedit/tst_qtextedit.cpp
@@ -1978,8 +1978,23 @@ void tst_QTextEdit::fullWidthSelection_data()
 #endif
 
 #ifdef QT_BUILD_INTERNAL
+
+// With the fix for QTBUG-78318 scaling of documentMargin is added. The testing framework
+// forces qt_defaultDpi() to always return 96 DPI. For systems where the actual DPI differs
+// (typically 72 DPI) this would now cause scaling of the documentMargin when
+// drawing QTextEdit into QImage. In order to avoid the need of multiple reference PNGs
+// for comparison we disable the Qt::AA_Use96Dpi attribute for these tests.
+
+struct ForceSystemDpiHelper {
+  ForceSystemDpiHelper() { QCoreApplication::setAttribute(Qt::AA_Use96Dpi, false); }
+  ~ForceSystemDpiHelper() { QCoreApplication::setAttribute(Qt::AA_Use96Dpi, old); }
+  bool old = QCoreApplication::testAttribute(Qt::AA_Use96Dpi);
+};
+
 void tst_QTextEdit::fullWidthSelection()
 {
+    ForceSystemDpiHelper useSystemDpi;
+
     QFETCH(int, cursorFrom);
     QFETCH(int, cursorTo);
     QFETCH(QString, imageFileName);
@@ -2048,6 +2063,8 @@ void tst_QTextEdit::fullWidthSelection()
 #ifdef QT_BUILD_INTERNAL
 void tst_QTextEdit::fullWidthSelection2()
 {
+    ForceSystemDpiHelper useSystemDpi;
+
     QPalette myPalette;
     myPalette.setColor(QPalette::All, QPalette::HighlightedText, QColor(0,0,0,0));
     myPalette.setColor(QPalette::All, QPalette::Highlight, QColor(239,221,85));