diff --git a/src/surfaceitem_internal.cpp b/src/surfaceitem_internal.cpp
index 52a46f8e42..29bb9a7a70 100644
--- a/src/surfaceitem_internal.cpp
+++ b/src/surfaceitem_internal.cpp
@@ -9,6 +9,8 @@
 #include "internalwindow.h"
 #include "scene.h"
 
+#include <QOpenGLFramebufferObject>
+
 namespace KWin
 {
 
@@ -71,9 +73,11 @@ void SurfacePixmapInternal::update()
 
     if (window->internalFramebufferObject()) {
         m_fbo = window->internalFramebufferObject();
+        m_size = m_fbo->size();
         m_hasAlphaChannel = true;
     } else if (!window->internalImageObject().isNull()) {
         m_rasterBuffer = window->internalImageObject();
+        m_size = m_rasterBuffer.size();
         m_hasAlphaChannel = m_rasterBuffer.hasAlphaChannel();
     }
 }
diff --git a/src/surfaceitem_wayland.cpp b/src/surfaceitem_wayland.cpp
index eb56e51e78..2199edb8d8 100644
--- a/src/surfaceitem_wayland.cpp
+++ b/src/surfaceitem_wayland.cpp
@@ -193,6 +193,7 @@ void SurfacePixmapWayland::setBuffer(KWaylandServer::ClientBuffer *buffer)
     if (m_buffer) {
         m_buffer->ref();
         m_hasAlphaChannel = m_buffer->hasAlphaChannel();
+        m_size = m_buffer->size();
     }
 }