diff --git a/src/kernel/synch.rs b/src/kernel/synch.rs
index 8a7fe98..a2038e6 100644
--- a/src/kernel/synch.rs
+++ b/src/kernel/synch.rs
@@ -26,7 +26,7 @@ impl Semaphore{
     pub fn v(&mut self, current_thread:Rc<Thread>, machine: &mut Machine){
         let old_status = machine.interrupt.set_status(InterruptOff);
         self.counter-=1;
-        if self.waiting_queue.peek == None {
+        if self.waiting_queue.peek() == None {
             self.waiting_queue.push(Rc::clone(&current_thread));
             current_thread.sleep();
         }