diff --git a/google-apis-core/lib/google/api_client/client_secrets.rb b/google-apis-core/lib/google/api_client/client_secrets.rb
index fb629bcce75..32142439bbb 100644
--- a/google-apis-core/lib/google/api_client/client_secrets.rb
+++ b/google-apis-core/lib/google/api_client/client_secrets.rb
@@ -119,7 +119,7 @@ def initialize(options={})
       # @return [String]
       #   JSON
       def to_json
-        return Json.dump(to_hash)
+        return JSON.dump(to_hash)
       end
 
       def to_hash
diff --git a/google-apis-core/spec/google/api_client/client_secrets_spec.rb b/google-apis-core/spec/google/api_client/client_secrets_spec.rb
index a842b771563..3d6c8392721 100644
--- a/google-apis-core/spec/google/api_client/client_secrets_spec.rb
+++ b/google-apis-core/spec/google/api_client/client_secrets_spec.rb
@@ -19,6 +19,14 @@
 FIXTURES_PATH = File.expand_path('../../../fixtures', __FILE__)
 
 RSpec.describe Google::APIClient::ClientSecrets do
+  describe '#to_json' do
+    let(:secrets) { described_class.new('installed' => { 'client_id' => 'example-client' }) }
+
+    it 'serializes the client secrets hash' do
+      expect(JSON.parse(secrets.to_json)).to eq(secrets.to_hash)
+    end
+  end
+
   describe '::new' do
     let(:filename) { File.join(FIXTURES_PATH, 'files', 'client_secrets.json') }
     let(:data) { File.open(filename, 'r') { |file| JSON.load(file.read) } }