diff --git a/artiq/firmware/runtime/sched.rs b/artiq/firmware/runtime/sched.rs
index 4c027e895..770ac3f6c 100644
--- a/artiq/firmware/runtime/sched.rs
+++ b/artiq/firmware/runtime/sched.rs
@@ -265,6 +265,7 @@ impl<'a> Io<'a> {
     }
 }
 
+#[derive(Clone)]
 pub struct Mutex(Urc<Cell<bool>>);
 
 impl Mutex {