diff --git a/examples/3d/transmission.rs b/examples/3d/transmission.rs
index af7fec8c0d..65862efb19 100644
--- a/examples/3d/transmission.rs
+++ b/examples/3d/transmission.rs
@@ -475,7 +475,7 @@ fn example_control_system(
     let randomize_colors = input.just_pressed(KeyCode::C);
 
     for (material_handle, controls) in &controllable {
-        let mut material = materials.get_mut(material_handle).unwrap();
+        let material = materials.get_mut(material_handle).unwrap();
         if controls.transmission {
             material.transmission = state.transmission;
             material.thickness = state.thickness;