diff --git a/.travis.yml b/.travis.yml
index 156c2e3..484dbae 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,3 +4,5 @@ rvm:
   - 2.0.0-p576
   - 2.1.3
 script: bundle exec rspec spec
+before_install:
+  - gem install bundler
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d685c1e..933f78a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 0.9.1
+
+* Added `convert_na_to_nil=true/false` option to Client#execute
+
 # 0.9.0
 
 * Added support for Github R repos through OpenCPU
diff --git a/lib/opencpu/client.rb b/lib/opencpu/client.rb
index 80c0ca0..e0ec4da 100644
--- a/lib/opencpu/client.rb
+++ b/lib/opencpu/client.rb
@@ -8,12 +8,29 @@ def initialize
     end
 
     def execute(package, function, options = {})
-      user   = options.fetch :user, :system
-      data   = options.fetch :data, {}
-      format = options.fetch :format, :json
-      github_remote = options.fetch :github_remote, false
+      user                      = options.fetch :user, :system
+      data                      = options.fetch :data, {}
+      format                    = options.fetch :format, :json
+      github_remote             = options.fetch :github_remote, false
+      should_convert_na_to_nil  = options.fetch :convert_na_to_nil, false
+
       process_query package_url(package, function, user, github_remote, :json), data, format do |response|
-        JSON.parse(response.body)
+        output = JSON.parse(response.body)
+        output = convert_na_to_nil(output) if should_convert_na_to_nil
+        output
+      end
+    end
+
+    def convert_na_to_nil(data)
+      case data
+      when 'NA'
+        nil
+      when Hash
+        data.each { |k, v| data[k] = convert_na_to_nil(v) }
+      when Array
+        data.map! { |v| convert_na_to_nil(v) }
+      else
+        data
       end
     end
 
diff --git a/spec/fixtures/vcr_cassettes/animation_flip_coin.yml b/spec/fixtures/vcr_cassettes/animation_flip_coin.yml
index 659cdec..c3ef592 100644
--- a/spec/fixtures/vcr_cassettes/animation_flip_coin.yml
+++ b/spec/fixtures/vcr_cassettes/animation_flip_coin.yml
@@ -3004,4 +3004,3 @@ http_interactions:
         \    \n"
     http_version: 
   recorded_at: Tue, 14 Oct 2014 18:51:02 GMT
-recorded_with: VCR 2.9.3
diff --git a/spec/fixtures/vcr_cassettes/response_with_na_values.yml b/spec/fixtures/vcr_cassettes/response_with_na_values.yml
new file mode 100644
index 0000000..340010b
--- /dev/null
+++ b/spec/fixtures/vcr_cassettes/response_with_na_values.yml
@@ -0,0 +1,61 @@
+---
+http_interactions:
+- request:
+    method: post
+    uri: https://public.opencpu.org/ocpu/library/base/R/identity/json
+    body:
+      encoding: UTF-8
+      string: x=data.frame(x%3D1%2Cy%3D1)
+    headers: {}
+  response:
+    status:
+      code: 200
+      message: OK
+    headers:
+      Server:
+      - nginx/1.4.6 (Ubuntu)
+      Date:
+      - Tue, 14 Oct 2014 19:01:39 GMT
+      Content-Type:
+      - application/json
+      Location:
+      - https://public.opencpu.org/ocpu/tmp/x0c19f32080/
+      Transfer-Encoding:
+      - chunked
+      Connection:
+      - keep-alive
+      Cache-Control:
+      - max-age=300, public
+      X-Ocpu-Session:
+      - x0c19f32080
+      Access-Control-Allow-Origin:
+      - "*"
+      Access-Control-Allow-Headers:
+      - Origin, Content-Type, Accept, Accept-Encoding, Cache-Control
+      Access-Control-Expose-Headers:
+      - Location, X-ocpu-session, Content-Type, Cache-Control
+      X-Ocpu-R:
+      - R version 3.1.1 (2014-07-10)
+      X-Ocpu-Locale:
+      - en_US.UTF-8
+      X-Ocpu-Time:
+      - 2014-10-14 12:01:39 PDT
+      X-Ocpu-Version:
+      - 1.4.4
+      X-Ocpu-Server:
+      - rApache
+      X-Ocpu-Cache:
+      - MISS
+    body:
+      encoding: UTF-8
+      string: |+
+        [
+          {
+            "x": "NA",
+            "y": "not_na" 
+          }
+        ]
+
+    http_version: 
+  recorded_at: Tue, 14 Oct 2014 19:01:39 GMT
+recorded_with: VCR 2.9.3
diff --git a/spec/lib/opencpu/client_spec.rb b/spec/lib/opencpu/client_spec.rb
index 4d30fb8..7835959 100644
--- a/spec/lib/opencpu/client_spec.rb
+++ b/spec/lib/opencpu/client_spec.rb
@@ -105,6 +105,15 @@
       end
     end
 
+    context 'na_to_nil = true option is given' do
+      it 'converts "na" values to nil' do
+        VCR.use_cassette :response_with_na_values do |cassette|
+          response = client.execute(:base, :identity, format: nil, data: {}, convert_na_to_nil: true)
+          expect(response).to eq [{"x"=>nil, "y"=>"not_na"}]
+        end
+      end
+    end
+
     context 'multipart form / file uploads' do
       it "works" do
         skip # vcr is broken for file uploads https://github.com/vcr/vcr/issues/441
@@ -190,6 +199,25 @@
     end
   end
 
+  describe "#convert_na_to_nil" do
+    let(:client) { described_class.new }
+
+    it "converts 'NA' values in hashes in arrays" do
+      res = client.convert_na_to_nil([4, {foo: 'NA'}])
+      expect(res[1][:foo]).to be_nil
+    end
+
+    it "converts 'NA' values in arrays in hashes" do
+      res = client.convert_na_to_nil(foo: [1, 'NA'])
+      expect(res[:foo][1]).to be_nil
+    end
+
+    it 'leaves other values alone' do
+      res = client.convert_na_to_nil(foo: [1, 'NOTNA'])
+      expect(res[:foo][1]).to eq 'NOTNA'
+    end
+  end
+
   describe '#request_options' do
     it 'uses verify_ssl setting' do
       expect(described_class.new.send(:request_options, {}, nil)[:verify]).to be_truthy