diff --git a/decorations/decorationrenderer.cpp b/decorations/decorationrenderer.cpp
--- a/decorations/decorationrenderer.cpp
+++ b/decorations/decorationrenderer.cpp
@@ -61,6 +61,8 @@
 QImage Renderer::renderToImage(const QRect &geo)
 {
     Q_ASSERT(m_client);
+    if (geo.isNull())
+        return QImage();
     QImage image(geo.width(), geo.height(), QImage::Format_ARGB32_Premultiplied);
     image.fill(Qt::transparent);
     QPainter p(&image);