diff --git a/abstract_backend.h b/abstract_backend.h
index 1d1d73a94a..8f531cea20 100644
--- a/abstract_backend.h
+++ b/abstract_backend.h
@@ -61,6 +61,9 @@ public:
     bool isReady() const {
         return m_ready;
     }
+    void setInitialWindowSize(const QSize &size) {
+        m_initialWindowSize = size;
+    }
 
     void pointerMotion(const QPointF &position, quint32 time);
     void pointerButtonPressed(quint32 button, quint32 time);
@@ -93,6 +96,9 @@ protected:
     }
     void repaint(const QRect &rect);
     void setReady(bool ready);
+    QSize initialWindowSize() const {
+        return m_initialWindowSize;
+    }
 
 private Q_SLOTS:
     void installThemeCursor(quint32 id, const QPoint &hotspot);
@@ -108,6 +114,7 @@ private:
     WaylandCursorTheme *m_cursorTheme = nullptr;
     bool m_handlesOutputs = false;
     bool m_ready = false;
+    QSize m_initialWindowSize;
 };
 
 }
diff --git a/backends/x11/x11windowed_backend.cpp b/backends/x11/x11windowed_backend.cpp
index e3f853d9b7..029ffb511f 100644
--- a/backends/x11/x11windowed_backend.cpp
+++ b/backends/x11/x11windowed_backend.cpp
@@ -45,10 +45,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 namespace KWin
 {
 
-X11WindowedBackend::X11WindowedBackend(const QByteArray &display, const QSize &size, QObject *parent)
+X11WindowedBackend::X11WindowedBackend(const QByteArray &display, QObject *parent)
     : AbstractBackend(parent)
     , m_displayName(display)
-    , m_size(size)
 {
 }
 
@@ -123,6 +122,7 @@ void X11WindowedBackend::createWindow()
         XCB_EVENT_MASK_STRUCTURE_NOTIFY |
         XCB_EVENT_MASK_EXPOSURE
     };
+    m_size = initialWindowSize();
     xcb_create_window(m_connection, XCB_COPY_FROM_PARENT, m_window, m_screen->root,
                       0, 0, m_size.width(), m_size.height(),
                       0, XCB_WINDOW_CLASS_INPUT_OUTPUT, XCB_COPY_FROM_PARENT, mask, values);
diff --git a/backends/x11/x11windowed_backend.h b/backends/x11/x11windowed_backend.h
index 900b34b57f..87491435f0 100644
--- a/backends/x11/x11windowed_backend.h
+++ b/backends/x11/x11windowed_backend.h
@@ -39,7 +39,7 @@ class KWIN_EXPORT X11WindowedBackend : public AbstractBackend
     Q_OBJECT
     Q_PROPERTY(QSize size READ size NOTIFY sizeChanged)
 public:
-    X11WindowedBackend(const QByteArray &display, const QSize &size, QObject *parent);
+    X11WindowedBackend(const QByteArray &display, QObject *parent);
     virtual ~X11WindowedBackend();
     void init() override;
 
diff --git a/main_wayland.cpp b/main_wayland.cpp
index 4fdbca6313..f03366a50a 100644
--- a/main_wayland.cpp
+++ b/main_wayland.cpp
@@ -105,7 +105,7 @@ void ApplicationWayland::createBackend()
             backend = b;
         }
         if (!backend && !m_x11Display.isEmpty()) {
-            KWin::X11WindowedBackend *x11Backend = new KWin::X11WindowedBackend(m_x11Display, m_backendSize, this);
+            KWin::X11WindowedBackend *x11Backend = new KWin::X11WindowedBackend(m_x11Display, this);
             backend = x11Backend;
         }
     }
@@ -129,6 +129,7 @@ void ApplicationWayland::createBackend()
                 ::exit(1);
             }
         );
+        backend->setInitialWindowSize(m_backendSize);
         backend->init();
     } else {
         std::cerr <<  "FATAL ERROR: could not create a backend, exiting now" << std::endl;