diff --git a/lib/sidekiq/core_ext.rb b/lib/sidekiq/core_ext.rb
index 1de78e3a..959b52f4 100644
--- a/lib/sidekiq/core_ext.rb
+++ b/lib/sidekiq/core_ext.rb
@@ -54,14 +54,14 @@ begin
 rescue LoadError
   class Hash
     def stringify_keys
-      keys.each do |key|
+      each_key do |key|
         self[key.to_s] = delete(key)
       end
       self
     end if !{}.respond_to?(:stringify_keys)
 
     def symbolize_keys
-      keys.each do |key|
+      each_key do |key|
         self[(key.to_sym rescue key) || key] = delete(key)
       end
       self