diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index b49b47989a..ff1894807d 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -4994,7 +4994,8 @@ void QImage::convertToColorSpace(const QColorSpace &colorSpace)
         qWarning() << "QImage::convertToColorSpace: Output colorspace is not valid";
         return;
     }
-    detach();
+    if (d->colorSpace == colorSpace)
+        return;
     applyColorTransform(d->colorSpace.transformationToColorSpace(colorSpace));
     d->colorSpace = colorSpace;
 }
@@ -5036,6 +5037,7 @@ QColorSpace QImage::colorSpace() const
 */
 void QImage::applyColorTransform(const QColorTransform &transform)
 {
+    detach();
     if (!d)
         return;
     if (pixelFormat().colorModel() == QPixelFormat::Indexed) {
@@ -5078,14 +5080,14 @@ void QImage::applyColorTransform(const QColorTransform &transform)
     if (depth() > 32) {
         transformSegment = [&](int yStart, int yEnd) {
             for (int y = yStart; y < yEnd; ++y) {
-                QRgba64 *scanline = reinterpret_cast<QRgba64 *>(scanLine(y));
+                QRgba64 *scanline = reinterpret_cast<QRgba64 *>(d->data + y * d->bytes_per_line);
                 transform.d->apply(scanline, scanline, width(), flags);
             }
         };
     } else {
         transformSegment = [&](int yStart, int yEnd) {
             for (int y = yStart; y < yEnd; ++y) {
-                QRgb *scanline = reinterpret_cast<QRgb *>(scanLine(y));
+                QRgb *scanline = reinterpret_cast<QRgb *>(d->data + y * d->bytes_per_line);
                 transform.d->apply(scanline, scanline, width(), flags);
             }
         };