diff --git a/LibGUI/GEvent.h b/LibGUI/GEvent.h
index a0cdff198c8..5f1527c5a2a 100644
--- a/LibGUI/GEvent.h
+++ b/LibGUI/GEvent.h
@@ -56,15 +56,19 @@ public:
 
 class GPaintEvent final : public GEvent {
 public:
-    explicit GPaintEvent(const Rect& rect = Rect())
+    explicit GPaintEvent(const Rect& rect, const Size& window_size = Size())
         : GEvent(GEvent::Paint)
         , m_rect(rect)
+        , m_window_size(window_size)
     {
     }
 
-    const Rect& rect() const { return m_rect; }
+    Rect rect() const { return m_rect; }
+    Size window_size() const { return m_window_size; }
+
 private:
     Rect m_rect;
+    Size m_window_size;
 };
 
 class GResizeEvent final : public GEvent {
diff --git a/LibGUI/GEventLoop.cpp b/LibGUI/GEventLoop.cpp
index 2e0a2ba4c9c..d1353e433cf 100644
--- a/LibGUI/GEventLoop.cpp
+++ b/LibGUI/GEventLoop.cpp
@@ -119,7 +119,7 @@ void GEventLoop::handle_paint_event(const WSAPI_ServerMessage& event, GWindow& w
 #ifdef GEVENTLOOP_DEBUG
     dbgprintf("WID=%x Paint [%d,%d %dx%d]\n", event.window_id, event.paint.rect.location.x, event.paint.rect.location.y, event.paint.rect.size.width, event.paint.rect.size.height);
 #endif
-    post_event(window, make<GPaintEvent>(event.paint.rect));
+    post_event(window, make<GPaintEvent>(event.paint.rect, event.paint.window_size));
 }
 
 void GEventLoop::handle_resize_event(const WSAPI_ServerMessage& event, GWindow& window)
diff --git a/LibGUI/GWindow.cpp b/LibGUI/GWindow.cpp
index 0b61f922cfa..7bcca700152 100644
--- a/LibGUI/GWindow.cpp
+++ b/LibGUI/GWindow.cpp
@@ -168,9 +168,9 @@ void GWindow::event(GEvent& event)
         auto rect = paint_event.rect();
         bool created_new_backing_store = !m_backing;
         if (!m_backing) {
-            // NOTE: size() may change at any time since it's synchronously retrieved from the WindowServer.
             ASSERT(GEventLoop::main().server_pid());
-            Size new_backing_store_size = size();
+            ASSERT(!paint_event.window_size().is_empty());
+            Size new_backing_store_size = paint_event.window_size();
             size_t size_in_bytes = new_backing_store_size.area() * sizeof(RGBA32);
             void* buffer;
             int shared_buffer_id = create_shared_buffer(GEventLoop::main().server_pid(), size_in_bytes, (void**)&buffer);
diff --git a/WindowServer/WSAPITypes.h b/WindowServer/WSAPITypes.h
index 9084190ad7f..e7fd570809f 100644
--- a/WindowServer/WSAPITypes.h
+++ b/WindowServer/WSAPITypes.h
@@ -101,6 +101,7 @@ struct WSAPI_ServerMessage {
         } window;
         struct {
             WSAPI_Rect rect;
+            WSAPI_Size window_size;
         } paint;
         struct {
             WSAPI_Point position;
diff --git a/WindowServer/WSClientConnection.cpp b/WindowServer/WSClientConnection.cpp
index 2e5fcf5e075..0cf421b0f4e 100644
--- a/WindowServer/WSClientConnection.cpp
+++ b/WindowServer/WSClientConnection.cpp
@@ -349,10 +349,12 @@ void WSClientConnection::handle_request(WSAPIInvalidateRectRequest& request)
         post_error("Bad window ID");
         return;
     }
+    auto& window = *(*it).value;
     WSAPI_ServerMessage response;
     response.type = WSAPI_ServerMessage::Type::Paint;
     response.window_id = window_id;
     response.paint.rect = request.rect();
+    response.paint.window_size = window.size();
     post_message(response);
 }