diff --git a/spec/integration/custom_attributes_spec.rb b/spec/integration/custom_attributes_spec.rb
index 3473d024..3f3edc8b 100644
--- a/spec/integration/custom_attributes_spec.rb
+++ b/spec/integration/custom_attributes_spec.rb
@@ -4,6 +4,26 @@
 
   before do
     module Examples
+      class ExternalObjectId
+        attr_reader :oid
+        include Equalizer.new(:oid)
+        def initialize(oid)
+          @oid = oid
+        end
+
+        def self.from_string(oid)
+          new(oid)
+        end
+      end
+
+      class ExternalObjectIdAttribute < Virtus::Attribute
+        primitive ExternalObjectId
+
+        def coerce(input)
+          ExternalObjectId.from_string(input.to_s)
+        end
+      end
+
       class NoisyString < Virtus::Attribute
         lazy true
 
@@ -22,6 +42,9 @@ class User
         attribute :name, String
         attribute :scream, NoisyString
         attribute :expression, RegularExpression
+        attribute :id, ExternalObjectId
+        attribute :other_ids, Array[ExternalObjectId]
+        attribute :alias_ids, Hash[ExternalObjectId => ExternalObjectId]
       end
     end
   end
@@ -39,4 +62,36 @@ class User
     expect(subject.scream).to eq('WELCOME')
   end
 
+  context 'with a primitive defined' do
+    specify 'allows you to define coercion methods' do
+      subject.id = '53e51e803f30e1037e0008ac'
+      expect(subject.id).to eq(
+        Examples::ExternalObjectId.from_string('53e51e803f30e1037e0008ac')
+      )
+    end
+
+    context 'when used as an array member' do
+      specify 'coerces array members' do
+        subject.other_ids = [
+          '53e51eee3f30e1037e002c01', '53e51eee3f30e1037e002c02'
+        ]
+
+        expect(subject.other_ids).to eq([
+          Examples::ExternalObjectId.from_string('53e51eee3f30e1037e002c01'),
+          Examples::ExternalObjectId.from_string('53e51eee3f30e1037e002c02')
+        ])
+      end
+    end
+
+    context 'when used as a Hash key and/or value members' do
+      specify 'coerces key and value members' do
+        subject.alias_ids = { :one => 'two', 'three' => :four }
+        expect(subject.alias_ids).to eq({ 
+          Examples::ExternalObjectId.from_string('one') => Examples::ExternalObjectId.from_string('two'),
+          Examples::ExternalObjectId.from_string('three') => Examples::ExternalObjectId.from_string('four')
+        })
+      end
+    end
+  end
+
 end