diff --git a/BasiliskII/src/Unix/timer_unix.cpp b/BasiliskII/src/Unix/timer_unix.cpp
index 684edec6..cac3d585 100644
--- a/BasiliskII/src/Unix/timer_unix.cpp
+++ b/BasiliskII/src/Unix/timer_unix.cpp
@@ -333,16 +333,19 @@ void idle_wait(void)
 	pthread_mutex_unlock(&idle_lock);
 #else
 #ifdef IDLE_USES_SEMAPHORE
+	LOCK_IDLE;
 	if (idle_sem_ok < 0)
 		idle_sem_ok = (sem_init(&idle_sem, 0, 0) == 0);
 	if (idle_sem_ok > 0) {
-		LOCK_IDLE;
 		idle_sem_ok++;
 		UNLOCK_IDLE;
 		sem_wait(&idle_sem);
 		return;
 	}
+	UNLOCK_IDLE;
 #endif
+
+	// Fallback: sleep 10 ms
 	Delay_usec(10000);
 #endif
 }
@@ -358,13 +361,14 @@ void idle_resume(void)
 	pthread_cond_signal(&idle_cond);
 #else
 #ifdef IDLE_USES_SEMAPHORE
+	LOCK_IDLE;
 	if (idle_sem_ok > 1) {
-		LOCK_IDLE;
 		idle_sem_ok--;
 		UNLOCK_IDLE;
 		sem_post(&idle_sem);
 		return;
 	}
+	UNLOCK_IDLE;
 #endif
 #endif
 }