diff --git a/lib/garner/cache/identity.rb b/lib/garner/cache/identity.rb
index 131d433..147ed79 100644
--- a/lib/garner/cache/identity.rb
+++ b/lib/garner/cache/identity.rb
@@ -11,8 +11,8 @@ def initialize(ruby_context = nil)
         @key_hash = {}
 
         # Set up options hash with defaults
-        @options_hash = Garner.config.global_cache_options || {}
-        @options_hash.merge!(expires_in: Garner.config.expires_in)
+        @options_hash = Garner.config.global_cache_options.dup || {}
+        @options_hash[:expires_in] ||= Garner.config.expires_in
       end
 
       def fetch(&block)
diff --git a/spec/garner/cache/identity_spec.rb b/spec/garner/cache/identity_spec.rb
index bc2e4db..682024b 100644
--- a/spec/garner/cache/identity_spec.rb
+++ b/spec/garner/cache/identity_spec.rb
@@ -6,6 +6,13 @@
     expect(subject.options_hash[:foo]).to eq 'bar'
   end
 
+  it 'includes Garner.config.global_cache_options[:expires_in]' do
+    Garner.configure do |config|
+      config.global_cache_options = { expires_in: 5.minutes }
+    end
+    subject.options_hash[:expires_in].should eq 5.minutes
+  end
+
   it 'includes Garner.config.expires_in' do
     Garner.configure { |config| config.expires_in = 5.minutes }
     expect(subject.options_hash[:expires_in]).to eq 5.minutes