diff --git a/src/backends/x11/windowed/egl_x11_backend.cpp b/src/backends/x11/windowed/egl_x11_backend.cpp
index 67c9fb5a6f..2f5f75c2f8 100644
--- a/src/backends/x11/windowed/egl_x11_backend.cpp
+++ b/src/backends/x11/windowed/egl_x11_backend.cpp
@@ -23,7 +23,6 @@ namespace KWin
 
 EglX11Output::EglX11Output(EglX11Backend *backend, Output *output, EGLSurface surface)
     : m_eglSurface(surface)
-    , m_fbo(new GLFramebuffer(0, output->pixelSize()))
     , m_output(output)
     , m_backend(backend)
 {
@@ -34,9 +33,17 @@ EglX11Output::~EglX11Output()
     eglDestroySurface(m_backend->eglDisplay(), m_eglSurface);
 }
 
+void EglX11Output::ensureFbo()
+{
+    if (!m_fbo || m_fbo->size() != m_output->pixelSize()) {
+        m_fbo.reset(new GLFramebuffer(0, m_output->pixelSize()));
+    }
+}
+
 OutputLayerBeginFrameInfo EglX11Output::beginFrame()
 {
     eglMakeCurrent(m_backend->eglDisplay(), m_eglSurface, m_eglSurface, m_backend->context());
+    ensureFbo();
     GLFramebuffer::pushFramebuffer(m_fbo.data());
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(m_fbo.data()),
diff --git a/src/backends/x11/windowed/egl_x11_backend.h b/src/backends/x11/windowed/egl_x11_backend.h
index 54f393bdca..f160749fe7 100644
--- a/src/backends/x11/windowed/egl_x11_backend.h
+++ b/src/backends/x11/windowed/egl_x11_backend.h
@@ -32,6 +32,8 @@ public:
     QRegion lastDamage() const;
 
 private:
+    void ensureFbo();
+
     EGLSurface m_eglSurface;
     QScopedPointer<GLFramebuffer> m_fbo;
     QRegion m_lastDamage;
diff --git a/src/backends/x11/windowed/scene_qpainter_x11_backend.cpp b/src/backends/x11/windowed/scene_qpainter_x11_backend.cpp
index 6d022506fc..e670e8941d 100644
--- a/src/backends/x11/windowed/scene_qpainter_x11_backend.cpp
+++ b/src/backends/x11/windowed/scene_qpainter_x11_backend.cpp
@@ -18,14 +18,23 @@ namespace KWin
 
 X11WindowedQPainterOutput::X11WindowedQPainterOutput(Output *output, xcb_window_t window)
     : window(window)
-    , buffer(output->pixelSize() * output->scale(), QImage::Format_RGB32)
     , m_output(output)
 {
-    buffer.fill(Qt::black);
+}
+
+void X11WindowedQPainterOutput::ensureBuffer()
+{
+    const QSize nativeSize(m_output->pixelSize() * m_output->scale());
+
+    if (buffer.size() != nativeSize) {
+        buffer = QImage(nativeSize, QImage::Format_RGB32);
+        buffer.fill(Qt::black);
+    }
 }
 
 OutputLayerBeginFrameInfo X11WindowedQPainterOutput::beginFrame()
 {
+    ensureBuffer();
     return OutputLayerBeginFrameInfo{
         .renderTarget = RenderTarget(&buffer),
         .repaint = m_output->rect(),
diff --git a/src/backends/x11/windowed/scene_qpainter_x11_backend.h b/src/backends/x11/windowed/scene_qpainter_x11_backend.h
index 88c2badcc3..76a12cbb20 100644
--- a/src/backends/x11/windowed/scene_qpainter_x11_backend.h
+++ b/src/backends/x11/windowed/scene_qpainter_x11_backend.h
@@ -29,6 +29,8 @@ class X11WindowedQPainterOutput : public OutputLayer
 public:
     X11WindowedQPainterOutput(Output *output, xcb_window_t window);
 
+    void ensureBuffer();
+
     OutputLayerBeginFrameInfo beginFrame() override;
     void endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion) override;
 
diff --git a/src/backends/x11/windowed/x11windowed_output.cpp b/src/backends/x11/windowed/x11windowed_output.cpp
index ceeb1b78de..86394aed28 100644
--- a/src/backends/x11/windowed/x11windowed_output.cpp
+++ b/src/backends/x11/windowed/x11windowed_output.cpp
@@ -66,9 +66,6 @@ void X11WindowedOutput::init(const QPoint &logicalPosition, const QSize &pixelSi
     m_renderLoop->setRefreshRate(refreshRate);
     m_vsyncMonitor->setRefreshRate(refreshRate);
 
-    auto mode = QSharedPointer<OutputMode>::create(pixelSize, refreshRate);
-    setModesInternal({mode}, mode);
-
     setGeometry(logicalPosition, pixelSize);
     setScale(m_backend->initialOutputScale());
 
@@ -150,8 +147,9 @@ void X11WindowedOutput::initXInputForWindow()
 
 void X11WindowedOutput::setGeometry(const QPoint &logicalPosition, const QSize &pixelSize)
 {
-    // TODO: set mode to have updated pixelSize
-    Q_UNUSED(pixelSize);
+    auto mode = QSharedPointer<OutputMode>::create(pixelSize, m_renderLoop->refreshRate());
+    setModesInternal({mode}, mode);
+
     moveTo(logicalPosition);
 }