diff --git a/lib/rufus/sc/scheduler.rb b/lib/rufus/sc/scheduler.rb
index <HASH>..<HASH> 100644
--- a/lib/rufus/sc/scheduler.rb
+++ b/lib/rufus/sc/scheduler.rb
@@ -423,7 +423,7 @@ module Rufus::Scheduler
       when Array
         mutex.reduce(block) do |memo, m|
           m = (@mutexes[m.to_s] ||= Mutex.new) unless m.is_a?(Mutex)
-          -> { m.synchronize { memo.call } }
+          lambda { m.synchronize { memo.call } }
         end.call
       else
         (@mutexes[mutex.to_s] ||= Mutex.new).synchronize { block.call }
use lambda instead of ->, be friendly to <I>

rufus-scheduler has been around for a while, there are certainly lots of deployments out there still running on <I>.x, they don't get "->".