diff --git a/arm/async.h b/arm/async.h
index 589380e..a5b80c4 100644
--- a/arm/async.h
+++ b/arm/async.h
@@ -205,7 +205,7 @@ void schedule(std::coroutine_handle<> h, int ms = 0);
 void enqueue(std::coroutine_handle<> h, AwaitableType type);
 void resume(AwaitableType type);  // typically called from an ISR
 
-void main_loop(void (*idle_function)());
+void main_loop(bool (*idle_function)());
 
 inline auto await(AwaitableType type) {
     struct awaitable {