diff --git a/src/mad/ruby/ActionManager.rb b/src/mad/ruby/ActionManager.rb
index 4f62a2d4f6..213fdafcf4 100644
--- a/src/mad/ruby/ActionManager.rb
+++ b/src/mad/ruby/ActionManager.rb
@@ -144,7 +144,7 @@ class ActionManager
             thread = @action_running[action_id]
             
             if thread
-                thread.kill!
+                thread.kill
 
                 @num_running -= 1
                 @action_running.delete(action_id)