diff --git a/test/fiber/scheduler.rb b/test/fiber/scheduler.rb
index c685e6ffc0..6e04409c6e 100644
--- a/test/fiber/scheduler.rb
+++ b/test/fiber/scheduler.rb
@@ -24,6 +24,8 @@ class Scheduler
     @lock = Mutex.new
     @blocking = 0
     @ready = []
+
+    @urgent = nil
   end
 
   attr :readable