diff --git a/lib/montrose/recurrence.rb b/lib/montrose/recurrence.rb
index <HASH>..<HASH> 100644
--- a/lib/montrose/recurrence.rb
+++ b/lib/montrose/recurrence.rb
@@ -50,7 +50,7 @@ module Montrose
     alias to_h to_hash
 
     def inspect
-      "#<#{self.class}:#{object_id} #{to_h.inspect}>"
+      "#<#{self.class}:#{object_id.to_s(16)} #{to_h.inspect}>"
     end
 
     private
diff --git a/spec/montrose/recurrence_spec.rb b/spec/montrose/recurrence_spec.rb
index <HASH>..<HASH> 100644
--- a/spec/montrose/recurrence_spec.rb
+++ b/spec/montrose/recurrence_spec.rb
@@ -123,7 +123,7 @@ describe Montrose::Recurrence do
     let(:recurrence) { new_recurrence(every: :month, starts: now) }
 
     it do
-      inspected = "#<Montrose::Recurrence:#{recurrence.object_id} "
+      inspected = "#<Montrose::Recurrence:#{recurrence.object_id.to_s(16)} "
       inspected << "{:every=>:month, :starts=>#{now.inspect}, :interval=>1}>"
       recurrence.inspect.must_equal inspected
     end
Format inspect method object_id with base <I>