diff --git a/jupyros/pubsub.py b/jupyros/pubsub.py
index 4bf86c6..a588f5e 100644
--- a/jupyros/pubsub.py
+++ b/jupyros/pubsub.py
@@ -47,7 +47,7 @@ def subscribe(topic, msg_type, callback):
     """
 
     if subscriber_registry.get(topic):
-        raise Error("Already registerd...")
+        raise RuntimeError("Already registerd...")
 
     out = widgets.Output(layout={'border': '1px solid gray'})
     subscriber_registry[topic] = rospy.Subscriber(topic, msg_type, callback)
@@ -68,4 +68,4 @@ def stop_start_subscriber(x):
     btn.on_click(stop_start_subscriber)
     btns = widgets.HBox((btn, ))
     vbox = widgets.VBox((btns, out))
-    return vbox
\ No newline at end of file
+    return vbox