diff --git a/egui/src/app.rs b/egui/src/app.rs
index 4417180b..be79497d 100644
--- a/egui/src/app.rs
+++ b/egui/src/app.rs
@@ -56,6 +56,9 @@ pub struct AppOutput {
     /// This does nothing for web apps.
     pub quit: bool,
 
+    /// Set to some size to resize the outer window (e.g. glium window) to this size.
+    pub window_size: Option<crate::Vec2>,
+
     /// If the app sets this, change the `pixels_per_point` of Egui to this next frame.
     pub pixels_per_point: Option<f32>,
 }
diff --git a/egui_glium/src/backend.rs b/egui_glium/src/backend.rs
index be1a5a8f..82a2f4c4 100644
--- a/egui_glium/src/backend.rs
+++ b/egui_glium/src/backend.rs
@@ -88,13 +88,25 @@ pub fn run(
             {
                 let egui::app::AppOutput {
                     quit,
+                    window_size,
                     pixels_per_point,
                 } = app_output;
+
                 if let Some(pixels_per_point) = pixels_per_point {
                     // User changed GUI scale
                     raw_input.pixels_per_point = Some(pixels_per_point);
                 }
 
+                if let Some(window_size) = window_size {
+                    display
+                        .gl_window()
+                        .window()
+                        .set_inner_size(glutin::dpi::LogicalSize {
+                            width: window_size.x,
+                            height: window_size.y,
+                        });
+                }
+
                 *control_flow = if quit {
                     glutin::event_loop::ControlFlow::Exit
                 } else if egui_output.needs_repaint {
diff --git a/egui_web/src/backend.rs b/egui_web/src/backend.rs
index e26a5b00..cf040d2a 100644
--- a/egui_web/src/backend.rs
+++ b/egui_web/src/backend.rs
@@ -170,7 +170,8 @@ impl AppRunner {
 
         {
             let egui::app::AppOutput {
-                quit: _,
+                quit: _,        // Can't quit a web page
+                window_size: _, // Can't resize a web page
                 pixels_per_point,
             } = app_output;