diff --git a/spec/concurrent/timer_task_spec.rb b/spec/concurrent/timer_task_spec.rb
index 1690cd73e..24610b916 100644
--- a/spec/concurrent/timer_task_spec.rb
+++ b/spec/concurrent/timer_task_spec.rb
@@ -129,7 +129,7 @@ def trigger_observable(observable)
       it 'raises an exception if no block given' do
         expect {
           Concurrent::TimerTask.execute
-        }.to raise_error
+        }.to raise_error(ArgumentError)
       end
 
       specify '#execution_interval is writeable' do