diff --git a/sixtyfps_runtime/corelib/eventloop.rs b/sixtyfps_runtime/corelib/eventloop.rs
index 10e1dadcd..b9b07e7b1 100644
--- a/sixtyfps_runtime/corelib/eventloop.rs
+++ b/sixtyfps_runtime/corelib/eventloop.rs
@@ -58,7 +58,7 @@ pub trait GenericWindow {
     fn process_key_input(self: Rc<Self>, event: &KeyEvent);
     /// Calls the `callback` function with the underlying winit::Window that this
     /// GenericWindow backs.
-    fn with_platform_window(&self, callback: &dyn Fn(&winit::window::Window));
+    fn with_platform_window(&self, callback: &mut dyn FnMut(&winit::window::Window));
     /// Requests for the window to be mapped to the screen.
     ///
     /// Arguments:
@@ -271,9 +271,11 @@ impl EventLoop {
                         if let Some(Some(window)) =
                             windows.borrow().get(&window_id).map(|weakref| weakref.upgrade())
                         {
-                            window.with_platform_window(&|platform_window| {
-                                window.set_scale_factor(platform_window.scale_factor() as f32);
+                            let mut sf = 1.;
+                            window.with_platform_window(&mut |platform_window| {
+                                sf = platform_window.scale_factor();
                             });
+                            window.set_scale_factor(sf as f32);
                             window.set_width(size.width as f32);
                             window.set_height(size.height as f32);
                         }
diff --git a/sixtyfps_runtime/corelib/graphics.rs b/sixtyfps_runtime/corelib/graphics.rs
index 690a76eea..f7a6c8275 100644
--- a/sixtyfps_runtime/corelib/graphics.rs
+++ b/sixtyfps_runtime/corelib/graphics.rs
@@ -573,7 +573,7 @@ impl<Backend: GraphicsBackend> crate::eventloop::GenericWindow for GraphicsWindo
         }
     }
 
-    fn with_platform_window(&self, callback: &dyn Fn(&winit::window::Window)) {
+    fn with_platform_window(&self, callback: &mut dyn FnMut(&winit::window::Window)) {
         let map_state = self.map_state.borrow();
         let window = map_state.as_mapped();
         let backend = window.backend.borrow();