diff --git a/all-is-cubes-desktop/src/lib.rs b/all-is-cubes-desktop/src/lib.rs
index 5a6f1b95e..f18da077a 100644
--- a/all-is-cubes-desktop/src/lib.rs
+++ b/all-is-cubes-desktop/src/lib.rs
@@ -1,3 +1,4 @@
+#![feature(async_closure)]
 #![feature(never_type)]
 
 //! Components for creating a desktop application that renders interactive [`all_is_cubes`]
@@ -101,7 +102,7 @@ pub fn inner_main<Ren: Renderer, Win: Window>(
             .context("failed to configure session for recording")?;
     }
 
-    dsession.session.set_main_task(|mut ctx| async move {
+    dsession.session.set_main_task(async move |mut ctx| {
         let universe_result: Result<Universe, anyhow::Error> = match universe_future.await {
             Ok(Ok(u)) => Ok(u),
             Ok(Err(e)) => {
diff --git a/all-is-cubes-desktop/src/session.rs b/all-is-cubes-desktop/src/session.rs
index 7b9d40693..4bb9ee1f6 100644
--- a/all-is-cubes-desktop/src/session.rs
+++ b/all-is-cubes-desktop/src/session.rs
@@ -9,7 +9,7 @@ use all_is_cubes::universe::Universe;
 use all_is_cubes::universe::UniverseStepInfo;
 use all_is_cubes::util::ErrorChain;
 use all_is_cubes_render::camera::Viewport;
-use all_is_cubes_ui::apps::ExitMainTask;
+use all_is_cubes_ui::apps::{ExitMainTask, MainTaskContext};
 
 use crate::Session;
 
@@ -145,25 +145,26 @@ impl<Ren, Win: crate::glue::Window> DesktopSession<Ren, Win> {
 
         // TODO: Also make a way to do this that isn't replacing the main task,
         // or that defines a way for the existing main task to coordinate.
-        self.session.set_main_task(move |mut ctx| async move {
-            // TODO: Offer confirmation before replacing the current universe.
-            // TODO: Then open a progress-bar UI page while we load.
-
-            match loader_task.await.unwrap() {
-                Ok(universe) => {
-                    ctx.set_universe(universe);
-                }
-                Err(e) => {
-                    ctx.show_modal_message(arcstr::format!(
-                        "Failed to load file '{path}':\n{e}",
-                        path = path.display(),
-                        e = ErrorChain(&e),
-                    ));
+        self.session
+            .set_main_task(async move |mut ctx: MainTaskContext| {
+                // TODO: Offer confirmation before replacing the current universe.
+                // TODO: Then open a progress-bar UI page while we load.
+
+                match loader_task.await.unwrap() {
+                    Ok(universe) => {
+                        ctx.set_universe(universe);
+                    }
+                    Err(e) => {
+                        ctx.show_modal_message(arcstr::format!(
+                            "Failed to load file '{path}':\n{e}",
+                            path = path.display(),
+                            e = ErrorChain(&e),
+                        ));
+                    }
                 }
-            }
 
-            ExitMainTask
-        })
+                ExitMainTask
+            })
     }
 
     /// Set the “fixed” window title — the portion of the title not determined by the universe,
diff --git a/all-is-cubes-ui/src/apps/session.rs b/all-is-cubes-ui/src/apps/session.rs
index ac27608e9..9a8b1d9fe 100644
--- a/all-is-cubes-ui/src/apps/session.rs
+++ b/all-is-cubes-ui/src/apps/session.rs
@@ -1370,7 +1370,7 @@ mod tests {
         let mut cameras = session.create_cameras(ListenableSource::constant(Viewport::ARBITRARY));
         session.set_main_task({
             let noticed_step = noticed_step.clone();
-            move |mut ctx| async move {
+            async move |mut ctx: MainTaskContext| {
                 eprintln!("main task: waiting for new universe");
                 let new_universe = recv.await.unwrap();
                 ctx.set_universe(new_universe);
diff --git a/all-is-cubes-ui/src/lib.rs b/all-is-cubes-ui/src/lib.rs
index 648e9ad8a..18801f36d 100644
--- a/all-is-cubes-ui/src/lib.rs
+++ b/all-is-cubes-ui/src/lib.rs
@@ -1,3 +1,4 @@
+#![feature(async_closure)]
 #![feature(never_type)]
 #![feature(noop_waker)]
 #![feature(precise_capturing)]
diff --git a/test-renderers/tests/wgpu-render.rs b/test-renderers/tests/wgpu-render.rs
index 80e51b93a..d985a36ef 100644
--- a/test-renderers/tests/wgpu-render.rs
+++ b/test-renderers/tests/wgpu-render.rs
@@ -1,5 +1,7 @@
 //! Runs [`test_renderers::harness_main`] against [`all_is_cubes_gpu::in_wgpu`].
 
+#![feature(async_closure)]
+
 use clap::Parser as _;
 use tokio::sync::OnceCell;
 
@@ -29,7 +31,7 @@ async fn main() -> test_renderers::HarnessResult {
         RendererId::Wgpu,
         test_renderers::SuiteId::Renderers,
         test_renderers::test_cases::all_tests,
-        move || async move { get_factory().await.unwrap() },
+        async move || get_factory().await.unwrap(),
         parallelism,
     )
     .await