diff --git a/ports/macos/timer.c b/ports/macos/timer.c
index 96799a12ad5b52d8f5a91ca620b28c9189275f34..0accdad14eea4b7bc2968d4d6cb8fc9edfb87dea 100644
--- a/ports/macos/timer.c
+++ b/ports/macos/timer.c
@@ -42,7 +42,8 @@ void aes67_timer_init_system(void)
 
 void aes67_timer_deinit_system(void)
 {
-    dispatch_release(queue);
+    if (queue)
+        dispatch_release(queue);
 }
 
 void aes67_timer_init(struct aes67_timer *timer)