diff --git a/lib/elasticsearch/transport/client.rb b/lib/elasticsearch/transport/client.rb
index 2aa9134..9bd6859 100644
--- a/lib/elasticsearch/transport/client.rb
+++ b/lib/elasticsearch/transport/client.rb
@@ -102,6 +102,9 @@ def initialize(arguments={}, &block)
 
         @arguments[:transport_options].update(:request => { :timeout => @arguments[:request_timeout] } ) if @arguments[:request_timeout]
 
+        @arguments[:transport_options][:headers] ||= {}
+        @arguments[:transport_options][:headers].update 'Content-Type' => 'application/json' unless @arguments[:transport_options][:headers].keys.any? {|k| k.to_s.downcase =~ /content\-?\_?type/}
+
         @send_get_body_as = @arguments[:send_get_body_as] || 'GET'
 
         transport_class  = @arguments[:transport_class] || DEFAULT_TRANSPORT_CLASS
diff --git a/lib/elasticsearch/transport/transport/http/curb.rb b/lib/elasticsearch/transport/transport/http/curb.rb
index c46ff64..58c3d5c 100644
--- a/lib/elasticsearch/transport/transport/http/curb.rb
+++ b/lib/elasticsearch/transport/transport/http/curb.rb
@@ -43,7 +43,11 @@ def perform_request(method, path, params={}, body=nil)
           #
           def __build_connection(host, options={}, block=nil)
             client = ::Curl::Easy.new
-            client.headers = {'User-Agent' => "Curb #{Curl::CURB_VERSION}"}
+
+            headers = options[:headers] || {}
+            headers.update('User-Agent' => "Curb #{Curl::CURB_VERSION}")
+
+            client.headers = headers
             client.url     = __full_url(host)
 
             if host[:user]
diff --git a/test/unit/client_test.rb b/test/unit/client_test.rb
index 1baa1a2..bd5f8ea 100644
--- a/test/unit/client_test.rb
+++ b/test/unit/client_test.rb
@@ -73,6 +73,11 @@ def initialize(*); end
       assert_equal 120, client.transport.options[:transport_options][:request][:timeout]
     end
 
+    should "set the 'Content-Type' header to 'application/json' by default" do
+      client = Elasticsearch::Transport::Client.new
+      assert_equal 'application/json', client.transport.options[:transport_options][:headers]['Content-Type']
+    end
+
     context "when passed hosts" do
       should "have localhost by default" do
         c = Elasticsearch::Transport::Client.new
diff --git a/test/unit/transport_curb_test.rb b/test/unit/transport_curb_test.rb
index 06d8c9a..3dc3127 100644
--- a/test/unit/transport_curb_test.rb
+++ b/test/unit/transport_curb_test.rb
@@ -77,6 +77,12 @@ class Elasticsearch::Transport::Transport::HTTP::FaradayTest < Test::Unit::TestC
         assert_raise(ArgumentError) { @transport.perform_request 'FOOBAR', '/' }
       end
 
+      should "properly pass the Content-Type header option" do
+        transport = Curb.new :hosts => [ { :host => 'foobar', :port => 1234 } ], :options => { :transport_options => { :headers => { 'Content-Type' => 'foo/bar' } } }
+
+        assert_equal "foo/bar", transport.connections.first.connection.headers["Content-Type"]
+      end
+
       should "allow to set options for Curb" do
         transport = Curb.new :hosts => [ { :host => 'foobar', :port => 1234 } ] do |curl|
           curl.headers["User-Agent"] = "myapp-0.0"
diff --git a/test/unit/transport_faraday_test.rb b/test/unit/transport_faraday_test.rb
index 41ae3a8..d486d74 100644
--- a/test/unit/transport_faraday_test.rb
+++ b/test/unit/transport_faraday_test.rb
@@ -42,6 +42,17 @@ class Elasticsearch::Transport::Transport::HTTP::FaradayTest < Test::Unit::TestC
       @transport.perform_request 'POST', '/', {}, {:foo => 'bar'}
     end
 
+    should "properly pass the Content-Type header option" do
+      transport = Faraday.new :hosts => [ { :host => 'foobar', :port => 1234 } ], :options => { :transport_options => { :headers => { 'Content-Type' => 'foo/bar' } } }
+
+      transport.connections.first.connection.expects(:run_request).with do |method, url, body, headers|
+        assert_equal 'foo/bar', headers['Content-Type']
+        true
+      end.returns(stub_everything)
+
+      transport.perform_request 'GET', '/'
+    end
+
     should "serialize the request body" do
       @transport.connections.first.connection.expects(:run_request).returns(stub_everything)
       @transport.serializer.expects(:dump)