diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index cd743e4c..e1cb7c6a 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -460,8 +460,7 @@ module ActiveModel
 
     # Returns a json representation of the serializable
     # object including the root.
-    def as_json(options=nil)
-      options ||= {}
+    def as_json(options={})
       if root = options.fetch(:root, @options.fetch(:root, _root))
         @options[:hash] = hash = {}
         @options[:unique_values] = {}
@@ -477,33 +476,17 @@ module ActiveModel
     # object without the root.
     def serializable_hash
       instrument(:serialize, :serializer => self.class.name) do
-        node = attributes
+        @node = attributes
         instrument :associations do
-          include_associations!(node) if _embed
+          include_associations! if _embed
         end
-        node
+        @node
       end
     end
 
-    def include_associations!(node)
-      _associations.each do |attr, klass|
-        opts = { :node => node }
-
-        if options.include?(:include) || options.include?(:exclude)
-          opts[:include] = included_association?(attr)
-        end
-
-        include! attr, opts
-      end
-    end
-
-    def included_association?(name)
-      if options.key?(:include)
-        options[:include].include?(name)
-      elsif options.key?(:exclude)
-        !options[:exclude].include?(name)
-      else
-        true
+    def include_associations!
+      _associations.each_key do |name|
+        include! name
       end
     end
 
@@ -526,9 +509,17 @@ module ActiveModel
           @options[:unique_values] ||= {}
         end
 
-      node = options[:node]
+      node = options[:node] ||= @node
       value = options[:value]
 
+      if options[:include] == nil
+        if @options.key?(:include)
+          options[:include] = @options[:include].include?(name)
+        elsif @options.include?(:exclude)
+          options[:include] = !@options[:exclude].include?(name)
+        end
+      end
+
       association_class =
         if klass = _associations[name]
           klass
diff --git a/test/serializer_test.rb b/test/serializer_test.rb
index 8358178d..fc4ec7dc 100644
--- a/test/serializer_test.rb
+++ b/test/serializer_test.rb
@@ -37,10 +37,11 @@ class SerializerTest < ActiveModel::TestCase
     def initialize(attributes)
       super(attributes)
       self.comments ||= []
+      self.comments_disabled = false
       self.author = nil
     end
 
-    attr_accessor :comments, :author
+    attr_accessor :comments, :comments_disabled, :author
     def active_model_serializer; PostSerializer; end
   end
 
@@ -89,11 +90,6 @@ class SerializerTest < ActiveModel::TestCase
     end
   end
 
-  class PostSerializer < ActiveModel::Serializer
-    attributes :title, :body
-    has_many :comments, :serializer => CommentSerializer
-  end
-
   def test_scope_works_correct
     serializer = ActiveModel::Serializer.new :foo, :scope => :bar
     assert_equal serializer.scope, :bar
@@ -163,6 +159,11 @@ class SerializerTest < ActiveModel::TestCase
     }, hash)
   end
 
+  class PostSerializer < ActiveModel::Serializer
+    attributes :title, :body
+    has_many :comments, :serializer => CommentSerializer
+  end
+
   def test_has_many
     user = User.new
 
@@ -184,6 +185,48 @@ class SerializerTest < ActiveModel::TestCase
     }, post_serializer.as_json)
   end
 
+  class PostWithConditionalCommentsSerializer < ActiveModel::Serializer
+    root :post
+    attributes :title, :body
+    has_many :comments, :serializer => CommentSerializer
+
+    def include_associations!
+      include! :comments unless object.comments_disabled
+    end
+  end
+
+  def test_conditionally_included_associations
+    user = User.new
+
+    post = Post.new(:title => "New Post", :body => "Body of new post", :email => "tenderlove@tenderlove.com")
+    comments = [Comment.new(:title => "Comment1"), Comment.new(:title => "Comment2")]
+    post.comments = comments
+
+    post_serializer = PostWithConditionalCommentsSerializer.new(post, :scope => user)
+
+    # comments enabled
+    post.comments_disabled = false
+    assert_equal({
+      :post => {
+        :title => "New Post",
+        :body => "Body of new post",
+        :comments => [
+          { :title => "Comment1" },
+          { :title => "Comment2" }
+        ]
+      }
+    }, post_serializer.as_json)
+
+    # comments disabled
+    post.comments_disabled = true
+    assert_equal({
+      :post => {
+        :title => "New Post",
+        :body => "Body of new post"
+      }
+    }, post_serializer.as_json)
+  end
+
   class Blog < Model
     attr_accessor :author
   end