diff --git a/jsonapi_parser.gemspec b/jsonapi_parser.gemspec
index 9ae3903..ed6653a 100644
--- a/jsonapi_parser.gemspec
+++ b/jsonapi_parser.gemspec
@@ -17,9 +17,9 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(spec)/})
   spec.require_paths = ['lib']
 
-  spec.add_dependency 'json', '~>1.8'
+  spec.add_dependency 'json', '~> 1.8'
 
-  spec.add_development_dependency 'rake', '>=0.9'
-  spec.add_development_dependency 'rspec', '~>3.4'
+  spec.add_development_dependency 'rake', '>= 0.9'
+  spec.add_development_dependency 'rspec', '~> 3.4'
   spec.add_development_dependency 'simplecov'
 end
diff --git a/lib/jsonapi/include_directive.rb b/lib/jsonapi/include_directive.rb
index 7562e95..0f2884e 100644
--- a/lib/jsonapi/include_directive.rb
+++ b/lib/jsonapi/include_directive.rb
@@ -12,6 +12,8 @@ module JSONAPI
   # @example 'posts.**' # => Include related posts, and all the included
   #   posts' related resources, and their related resources, recursively.
   class IncludeDirective
+    attr_reader :options, :hash
+
     # @param include_args (see Parser.include_hash_from_include_args)
     def initialize(include_args, options = {})
       include_hash = Parser.parse_include_args(include_args)
@@ -40,6 +42,28 @@ def [](key)
       end
     end
 
+    # @param another_directive [IncludeDirective]
+    # @return [IncludeDirective]
+    def merge(other)
+      dup.merge!(other)
+    end
+
+    # @param another_directive [IncludeDirective]
+    # @return [IncludeDirective]
+    def merge!(other)
+      fail ArgumentError,
+           "parameter MUST be an IncludeDirective" unless
+          other.is_a?(IncludeDirective)
+
+      hash = to_hash
+      Parser.deep_merge!(hash, other.to_hash)
+
+      merge_result = IncludeDirective.new(hash, options)
+      @hash = merge_result.hash
+      @options = merge_result.options
+      self
+    end
+
     # @return [Hash{Symbol => Hash}]
     def to_hash
       @hash.each_with_object({}) do |(key, value), hash|
diff --git a/spec/merge_spec.rb b/spec/merge_spec.rb
new file mode 100644
index 0000000..2427005
--- /dev/null
+++ b/spec/merge_spec.rb
@@ -0,0 +1,41 @@
+require 'jsonapi/include_directive'
+
+describe JSONAPI::IncludeDirective, '.merge' do
+  it 'works' do
+    d1 = JSONAPI::IncludeDirective.new(
+        {
+            post: {
+                comments: {
+                    references: [:url]
+                },
+                author: [:address]
+            }
+        }
+    )
+    d2 = JSONAPI::IncludeDirective.new(
+        {
+            post: {
+                comments: [:length],
+                author: {},
+                created_at: {}
+            }
+        }
+    )
+    expected = JSONAPI::IncludeDirective.new(
+        {
+            post: {
+                comments: {
+                    references: [:url],
+                    length: {}
+                },
+                author: [:address],
+                created_at: {}
+            }
+        }
+    ).to_hash
+
+    expect(d1.merge(d2).to_hash).to eq(expected)
+    d1.merge!(d2)
+    expect(d1.to_hash).to eq(expected)
+  end
+end