diff --git a/.rubocop.yml b/.rubocop.yml
new file mode 100644
index 0000000..df71430
--- /dev/null
+++ b/.rubocop.yml
@@ -0,0 +1,8 @@
+Metrics/BlockLength:
+  Exclude:
+    - '*.gemspec'
+    - 'test/**/*.rb'
+
+Metrics/ClassLength:
+  Exclude:
+    - 'lib/money/bank/currencylayer_bank.rb'
diff --git a/Gemfile b/Gemfile
index da9a46e..fbabc83 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 
 gemspec
diff --git a/Rakefile b/Rakefile
index 2dcb56b..5e7d75b 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rake/testtask'
 require 'rubocop/rake_task'
 require 'inch/rake'
@@ -6,6 +8,7 @@ task default: [:test, :rubocop, 'doc:suggest']
 
 Rake::TestTask.new do |t|
   t.pattern = 'test/**/*_test.rb'
+  t.warning = false
 end
 task spec: :test
 
diff --git a/lib/money/bank/currencylayer_bank.rb b/lib/money/bank/currencylayer_bank.rb
index 618b9dd..c6666e8 100644
--- a/lib/money/bank/currencylayer_bank.rb
+++ b/lib/money/bank/currencylayer_bank.rb
@@ -1,10 +1,26 @@
 # encoding: UTF-8
+# frozen_string_literal: true
+
 require 'open-uri'
 require 'money'
 require 'json'
 
 # Money gem class
 class Money
+  # Build in memory rates store
+  module RatesStore
+    # Memory class
+    class Memory
+      # Add method to reset the build in memory store
+      # @param [Hash] rt Optional initial exchange rate data.
+      #
+      # @return [Object] store.
+      def reset!(rt = {})
+        transaction { @index = rt }
+      end
+    end
+  end
+
   # https://github.com/RubyMoney/money#exchange-rate-stores
   module Bank
     # Invalid cache, file not found or cache empty
@@ -14,14 +30,13 @@ class InvalidCache < StandardError; end
     class NoAccessKey < StandardError; end
 
     # CurrencylayerBank base class
-    # rubocop:disable Metrics/ClassLength
     class CurrencylayerBank < Money::Bank::VariableExchange
       # CurrencylayerBank url
-      CL_URL = 'http://apilayer.net/api/live'.freeze
+      CL_URL = 'http://apilayer.net/api/live'
       # CurrencylayerBank secure url
-      CL_SECURE_URL = CL_URL.gsub('http:', 'https:').freeze
+      CL_SECURE_URL = CL_URL.gsub('http:', 'https:')
       # Default base currency
-      CL_SOURCE = 'USD'.freeze
+      CL_SOURCE = 'USD'
 
       # Use https to fetch rates from CurrencylayerBank
       # CurrencylayerBank only allows http as connection
@@ -49,6 +64,10 @@ class CurrencylayerBank < Money::Bank::VariableExchange
       # Parsed CurrencylayerBank result as Hash
       attr_reader :rates
 
+      # Get the timestamp of rates in memory
+      # @return [Time] time object or nil
+      attr_reader :rates_mem_timestamp
+
       # Set the seconds after than the current rates are automatically expired
       # by default, they never expire.
       #
@@ -90,6 +109,7 @@ def ttl_in_seconds
       # Update all rates from CurrencylayerBank JSON
       # @return [Array] array of exchange rates
       def update_rates(straight = false)
+        store.reset!
         exchange_rates(straight).each do |exchange_rate|
           currency = exchange_rate.first[3..-1]
           rate = exchange_rate.last
@@ -97,11 +117,23 @@ def update_rates(straight = false)
           add_rate(source, currency, rate)
           add_rate(currency, source, 1.0 / rate)
         end
+        @rates_mem_timestamp = rates_timestamp
+      end
+
+      # Override Money `add_rate` method for caching
+      # @param [String] from_currency Currency ISO code. ex. 'USD'
+      # @param [String] to_currency Currency ISO code. ex. 'CAD'
+      # @param [Numeric] rate Rate to use when exchanging currencies.
+      #
+      # @return [Numeric] rate.
+      def add_rate(from_currency, to_currency, rate)
+        super
       end
 
       # Override Money `get_rate` method for caching
       # @param [String] from_currency Currency ISO code. ex. 'USD'
       # @param [String] to_currency Currency ISO code. ex. 'CAD'
+      # @param [Hash] opts Options hash to set special parameters.
       #
       # @return [Numeric] rate.
       def get_rate(from_currency, to_currency, opts = {}) # rubocop:disable all
@@ -135,12 +167,15 @@ def get_rate(from_currency, to_currency, opts = {}) # rubocop:disable all
         rate
       end
 
-      # Fetch new rates if cached rates are expired
+      # Fetch new rates if cached rates are expired or stale
       # @return [Boolean] true if rates are expired and updated from remote
       def expire_rates!
         if expired?
           update_rates(true)
           true
+        elsif stale?
+          update_rates
+          true
         else
           false
         end
@@ -152,6 +187,14 @@ def expired?
         Time.now > rates_expiration
       end
 
+      # Check if rates are stale
+      # Stale is true if rates are updated straight by another thread.
+      # The actual thread has always old rates in memory store.
+      # @return [Boolean] true if rates are stale
+      def stale?
+        rates_timestamp != rates_mem_timestamp
+      end
+
       # Source url of CurrencylayerBank
       # defined with access_key and secure_connection
       # @return [String] the remote API url
diff --git a/money-currencylayer-bank.gemspec b/money-currencylayer-bank.gemspec
index 2b6e488..9bd7db1 100644
--- a/money-currencylayer-bank.gemspec
+++ b/money-currencylayer-bank.gemspec
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 Gem::Specification.new do |s|
   s.name = 'money-currencylayer-bank'
-  s.version = '0.5.3'
+  s.version = '0.5.4'
   s.date = Time.now.utc.strftime('%Y-%m-%d')
   s.homepage = "http://github.com/phlegx/#{s.name}"
   s.authors = ['Egon Zemmer']
@@ -9,7 +11,7 @@ Gem::Specification.new do |s|
     'rates from currencylayer.com. Compatible with the money gem.'
   s.summary = 'A gem that calculates the exchange rate using published rates ' \
     'from currencylayer.com.'
-  s.extra_rdoc_files = %w(README.md)
+  s.extra_rdoc_files = %w[README.md]
   s.files = Dir['LICENSE', 'README.md', 'Gemfile', 'lib/**/*.rb',
                 'test/**/*']
   s.license = 'MIT'
@@ -19,12 +21,12 @@ Gem::Specification.new do |s|
   s.rubygems_version = '1.3.7'
   s.add_dependency 'money', '~> 6.7'
   s.add_dependency 'monetize', '~> 1.4'
-  s.add_dependency 'json', '~> 1.8'
+  s.add_dependency 'json', '>= 1.8'
   s.add_development_dependency 'minitest', '~> 5.8'
   s.add_development_dependency 'minitest-line', '~> 0.6'
   s.add_development_dependency 'rr', '~> 1.1'
-  s.add_development_dependency 'rake', '~>10.4'
+  s.add_development_dependency 'rake', '~>12.0'
   s.add_development_dependency 'timecop', '~>0.8.1'
-  s.add_development_dependency 'rubocop', '~>0.37.2'
+  s.add_development_dependency 'rubocop', '~>0.48.1'
   s.add_development_dependency 'inch', '~>0.7.1'
 end
diff --git a/test/currencylayer_bank_test.rb b/test/currencylayer_bank_test.rb
index 581ac8a..ac55089 100644
--- a/test/currencylayer_bank_test.rb
+++ b/test/currencylayer_bank_test.rb
@@ -1,4 +1,6 @@
 # encoding: UTF-8
+# frozen_string_literal: true
+
 require File.expand_path(File.join(File.dirname(__FILE__), 'test_helper'))
 
 describe Money::Bank::CurrencylayerBank do
@@ -208,9 +210,12 @@
         delimiter: ','
       }
       Money::Currency.register(wtf)
-      subject.add_rate('USD', 'WTF', 2)
-      subject.add_rate('WTF', 'USD', 2)
-      subject.exchange_with(5000.to_money('WTF'), 'USD').cents.wont_equal 0
+      Timecop.freeze(subject.rates_timestamp) do
+        subject.add_rate('USD', 'WTF', 2)
+        subject.add_rate('WTF', 'USD', 2)
+        subject.exchange_with(5000.to_money('WTF'), 'USD').cents
+        subject.exchange_with(5000.to_money('WTF'), 'USD').cents.wont_equal 0
+      end
     end
   end
 
@@ -232,9 +237,10 @@
       @old_usd_eur_rate = 0.655
       # see test/live.json +54
       @new_usd_eur_rate = 0.886584
-      subject.add_rate('USD', 'EUR', @old_usd_eur_rate)
       subject.cache = temp_cache_path
       stub(subject).source_url { data_path }
+      subject.update_rates
+      subject.add_rate('USD', 'EUR', @old_usd_eur_rate)
     end
 
     after do
diff --git a/test/test_helper.rb b/test/test_helper.rb
index d7ac273..708a378 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,4 +1,6 @@
 # encoding: UTF-8
+# frozen_string_literal: true
+
 require 'minitest/autorun'
 require 'rr'
 require 'money/bank/currencylayer_bank'