2 files changed, 27 insertions, 1 deletions
diff --git a/test/fiber/scheduler.rb b/test/fiber/scheduler.rb
index 1e7f60cdf0..f7a773ade1 100644
--- a/test/fiber/scheduler.rb
+++ b/test/fiber/scheduler.rb
@@ -93,6 +93,7 @@ class Scheduler
     end
   ensure
     @urgent.each(&:close)
+    @urgent = nil
   end
 
   def current_time
@@ -139,7 +140,7 @@ class Scheduler
     end
 
     if io = @urgent&.last
-      @urgent.last.write_nonblock('.')
+      io.write_nonblock('.')
     end
   end
 
diff --git a/test/fiber/test_mutex.rb b/test/fiber/test_mutex.rb
index 1f53ae1a1f..baec559a70 100644
--- a/test/fiber/test_mutex.rb
+++ b/test/fiber/test_mutex.rb
@@ -115,6 +115,31 @@ class TestFiberMutex < Test::Unit::TestCase
     assert processed == 3
   end
 
+  def test_queue_pop_waits
+    queue = Queue.new
+    running = false
+
+    thread = Thread.new do
+      scheduler = Scheduler.new
+      Thread.current.scheduler = scheduler
+
+      result = nil
+      Fiber.schedule do
+        result = queue.pop
+      end
+
+      running = true
+      scheduler.run
+      result
+    end
+
+    Thread.pass until running
+    sleep 0.1
+
+    queue << :done
+    assert_equal :done, thread.value
+  end
+
   def test_mutex_deadlock
     err = /No live threads left. Deadlock\?/
     assert_in_out_err %W[-I#{__dir__} -], <<-RUBY, ['in synchronize'], err, success: false