diff --git a/lib/facebook_ads/field_types.rb b/lib/facebook_ads/field_types.rb
index 6288279d..24f063dc 100644
--- a/lib/facebook_ads/field_types.rb
+++ b/lib/facebook_ads/field_types.rb
@@ -21,14 +21,21 @@
 module FacebookAds
   module FieldTypes
     def register(*type_names)
-      @@registry ||= {}
       type_names.each do |type_name|
-        @@registry[type_name] = self
+        registry[type_name] = self
       end
     end
 
     def lookup(type_name)
-      @@registry && @@registry[type_name]
+      if registry.has_key?(type_name)
+        registry[type_name]
+      elsif type_name.respond_to?(:include?) && type_name.include?('map<')
+        registry['map']
+      end
+    end
+
+    def registry
+      @@registry ||= {}
     end
 
     def for(type_spec)
diff --git a/lib/facebook_ads/field_types/object.rb b/lib/facebook_ads/field_types/object.rb
index b570bc46..326262bb 100644
--- a/lib/facebook_ads/field_types/object.rb
+++ b/lib/facebook_ads/field_types/object.rb
@@ -22,7 +22,7 @@ class Object < Base
       register 'hash', 'map', 'object'
 
       def deserialize(value, session = nil)
-        JSON.parse(value)
+        value.is_a?(String) ? JSON.parse(value) : value
       end
 
       def serialize(value)
diff --git a/spec/field_types/object_spec.rb b/spec/field_types/object_spec.rb
new file mode 100644
index 00000000..6756f967
--- /dev/null
+++ b/spec/field_types/object_spec.rb
@@ -0,0 +1,39 @@
+# Copyright (c) 2017-present, Facebook, Inc. All rights reserved.
+#
+# You are hereby granted a non-exclusive, worldwide, royalty-free license to use,
+# copy, modify, and distribute this software in source code or binary form for use
+# in connection with the web services and APIs provided by Facebook.
+#
+# As with any software that integrates with the Facebook platform, your use of
+# this software is subject to the Facebook Platform Policy
+# [http://developers.facebook.com/policy/]. This copyright notice shall be
+# included in all copies or substantial portions of the software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+# FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+# IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+require 'spec_helper'
+
+RSpec.describe FacebookAds::FieldTypes::Object do
+  subject(:this) { described_class.new }
+
+  describe '#deserialize' do
+    subject(:deserialize) { this.deserialize(value) }
+
+    context 'when given value is string type' do
+      let(:value) { "{\"ACTIONS\":200}" }
+
+      it { expect(deserialize).to eq({ "ACTIONS" => 200 }) }
+    end
+
+    context 'when given value is hash type' do
+      let(:value) { { "ACTIONS" => 200 } }
+
+      it { expect(deserialize).to eq({ "ACTIONS" => 200 }) }
+    end
+  end
+end
diff --git a/spec/file_types_spec.rb b/spec/file_types_spec.rb
new file mode 100644
index 00000000..ade77995
--- /dev/null
+++ b/spec/file_types_spec.rb
@@ -0,0 +1,52 @@
+# Copyright (c) 2017-present, Facebook, Inc. All rights reserved.
+#
+# You are hereby granted a non-exclusive, worldwide, royalty-free license to use,
+# copy, modify, and distribute this software in source code or binary form for use
+# in connection with the web services and APIs provided by Facebook.
+#
+# As with any software that integrates with the Facebook platform, your use of
+# this software is subject to the Facebook Platform Policy
+# [http://developers.facebook.com/policy/]. This copyright notice shall be
+# included in all copies or substantial portions of the software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+# FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+# COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+# IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+require 'spec_helper'
+
+RSpec.describe FacebookAds::FieldTypes do
+  subject(:this) { FacebookAds::FieldTypes }
+
+  describe '.lookup' do
+    subject(:lookup) { this.lookup(type) }
+
+    context 'when map<string, int> field type is given' do
+      let(:type) { 'map<string, int>' }
+      it { expect(lookup).to eq(FacebookAds::FieldTypes::Object) }
+    end
+
+    context 'when map<string, string> field type is given' do
+      let(:type) { 'map<string, string>' }
+      it { expect(lookup).to eq(FacebookAds::FieldTypes::Object) }
+    end
+
+    context 'when map field type is given' do
+      let(:type) { 'map' }
+      it { expect(lookup).to eq(FacebookAds::FieldTypes::Object) }
+    end
+
+    context 'when object field type is given' do
+      let(:type) { 'object' }
+      it { expect(lookup).to eq(FacebookAds::FieldTypes::Object) }
+    end
+
+    context 'when hash field type is given' do
+      let(:type) { 'hash' }
+      it { expect(lookup).to eq(FacebookAds::FieldTypes::Object) }
+    end
+  end
+end