diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index e9edf41a..f9c7e0b8 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -1,6 +1,6 @@
 require 'active_model/array_serializer'
 require 'active_model/serializable'
-require 'active_model/serializer/associations'
+require 'active_model/serializer/association'
 require 'active_model/serializer/config'
 
 require 'thread'
diff --git a/lib/active_model/serializer/associations.rb b/lib/active_model/serializer/association.rb
similarity index 62%
rename from lib/active_model/serializer/associations.rb
rename to lib/active_model/serializer/association.rb
index 44d7c84f..cdfe9195 100644
--- a/lib/active_model/serializer/associations.rb
+++ b/lib/active_model/serializer/association.rb
@@ -1,4 +1,6 @@
 require 'active_model/default_serializer'
+require 'active_model/serializer/association/has_one'
+require 'active_model/serializer/association/has_many'
 
 module ActiveModel
   class Serializer
@@ -49,54 +51,6 @@ module ActiveModel
       def build_serializer(object, options = {})
         serializer_class(object).new(object, options.merge(self.options))
       end
-
-      class HasOne < Association
-        def initialize(name, *args)
-          super
-          @root_key = @embedded_key.to_s.pluralize
-          @key ||= "#{name}_id"
-        end
-
-        def serializer_class(object)
-          serializer_from_options || serializer_from_object(object) || default_serializer
-        end
-
-        def build_serializer(object, options = {})
-          options[:_wrap_in_array] = embed_in_root?
-          super
-        end
-      end
-
-      class HasMany < Association
-        def initialize(name, *args)
-          super
-          @root_key = @embedded_key
-          @key ||= "#{name.to_s.singularize}_ids"
-        end
-
-        def serializer_class(object)
-          if use_array_serializer?
-            ArraySerializer
-          else
-            serializer_from_options
-          end
-        end
-
-        def options
-          if use_array_serializer?
-            { each_serializer: serializer_from_options }.merge! super
-          else
-            super
-          end
-        end
-
-        private
-
-        def use_array_serializer?
-          !serializer_from_options ||
-            serializer_from_options && !(serializer_from_options <= ArraySerializer)
-        end
-      end
     end
   end
 end
diff --git a/lib/active_model/serializer/association/has_many.rb b/lib/active_model/serializer/association/has_many.rb
new file mode 100644
index 00000000..4480afc6
--- /dev/null
+++ b/lib/active_model/serializer/association/has_many.rb
@@ -0,0 +1,36 @@
+module ActiveModel
+  class Serializer
+    class Association
+      class HasMany < Association
+        def initialize(name, *args)
+          super
+          @root_key = @embedded_key
+          @key ||= "#{name.to_s.singularize}_ids"
+        end
+
+        def serializer_class(object)
+          if use_array_serializer?
+            ArraySerializer
+          else
+            serializer_from_options
+          end
+        end
+
+        def options
+          if use_array_serializer?
+            { each_serializer: serializer_from_options }.merge! super
+          else
+            super
+          end
+        end
+
+        private
+
+        def use_array_serializer?
+          !serializer_from_options ||
+            serializer_from_options && !(serializer_from_options <= ArraySerializer)
+        end
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/lib/active_model/serializer/association/has_one.rb b/lib/active_model/serializer/association/has_one.rb
new file mode 100644
index 00000000..4965e428
--- /dev/null
+++ b/lib/active_model/serializer/association/has_one.rb
@@ -0,0 +1,22 @@
+module ActiveModel
+  class Serializer
+    class Association
+      class HasOne < Association
+        def initialize(name, *args)
+          super
+          @root_key = @embedded_key.to_s.pluralize
+          @key ||= "#{name}_id"
+        end
+
+        def serializer_class(object)
+          serializer_from_options || serializer_from_object(object) || default_serializer
+        end
+
+        def build_serializer(object, options = {})
+          options[:_wrap_in_array] = embed_in_root?
+          super
+        end
+      end
+    end
+  end
+end
\ No newline at end of file