diff --git a/lib/httparty.rb b/lib/httparty.rb
index 05e59282..f5a234e3 100644
--- a/lib/httparty.rb
+++ b/lib/httparty.rb
@@ -576,7 +576,7 @@ def perform_request(http_method, path, options, &block) #:nodoc:
     def process_headers(options)
       if options[:headers] && headers.any?
         options[:headers] = headers.merge(options[:headers])
-        options[:headers] = process_dynamic_headers(options[:headers])
+        options[:headers] = Utils.stringify_keys(process_dynamic_headers(options[:headers]))
       end
     end
 
@@ -654,6 +654,7 @@ def self.options(*args, &block)
 end
 
 require 'httparty/hash_conversions'
+require 'httparty/utils'
 require 'httparty/exceptions'
 require 'httparty/parser'
 require 'httparty/request'
diff --git a/lib/httparty/utils.rb b/lib/httparty/utils.rb
new file mode 100644
index 00000000..52578f8b
--- /dev/null
+++ b/lib/httparty/utils.rb
@@ -0,0 +1,11 @@
+module HTTParty
+  module Utils
+    def self.stringify_keys(hash)
+      return hash.transform_keys(&:to_s) if hash.respond_to?(:transform_keys)
+
+      hash.each_with_object({}) do |(key, value), new_hash|
+        new_hash[key.to_s] = value
+      end
+    end
+  end
+end
diff --git a/spec/httparty_spec.rb b/spec/httparty_spec.rb
index 1a64898a..8ac7bff0 100644
--- a/spec/httparty_spec.rb
+++ b/spec/httparty_spec.rb
@@ -153,33 +153,33 @@ def expect_headers(header = {})
     end
 
     it "uses the class headers when sending a request" do
-      expect_headers(foo: 'bar')
+      expect_headers('foo' => 'bar')
       @klass.headers(foo: 'bar')
       @klass.get('')
     end
 
     it "merges class headers with request headers" do
-      expect_headers(baz: 'spax', foo: 'bar')
+      expect_headers('baz' => 'spax', 'foo' => 'bar')
       @klass.headers(foo: 'bar')
       @klass.get('', headers: {baz: 'spax'})
     end
 
     it 'overrides class headers with request headers' do
-      expect_headers(baz: 'spax', foo: 'baz')
+      expect_headers('baz' => 'spax', 'foo' => 'baz')
       @klass.headers(foo: 'bar')
       @klass.get('', headers: {baz: 'spax', foo: 'baz'})
     end
 
     context "with cookies" do
       it 'utilizes the class-level cookies' do
-        expect_headers(foo: 'bar', 'cookie' => 'type=snickerdoodle')
+        expect_headers('foo' => 'bar', 'cookie' => 'type=snickerdoodle')
         @klass.headers(foo: 'bar')
         @klass.cookies(type: 'snickerdoodle')
         @klass.get('')
       end
 
       it 'adds cookies to the headers' do
-        expect_headers(foo: 'bar', 'cookie' => 'type=snickerdoodle')
+        expect_headers('foo' => 'bar', 'cookie' => 'type=snickerdoodle')
         @klass.headers(foo: 'bar')
         @klass.get('', cookies: {type: 'snickerdoodle'})
       end
@@ -213,6 +213,19 @@ def expect_headers(header = {})
         @klass.post('http://example.com', body: { file: File.open('spec/fixtures/tiny.gif')})
       end
     end
+
+    context 'when headers passed as symbols' do
+      let(:headers) { { 'foo' => 'application/json', 'bar' => 'example' } }
+
+      it 'converts them to string' do
+        expect(HTTParty::Request).to receive(:new)
+          .with(anything, anything, hash_including({ headers: headers }))
+          .and_return(double("mock response", perform: nil))
+
+        @klass.headers(foo: 'application/json')
+        @klass.post('http://example.com', headers: { bar: 'example' })
+      end
+    end
   end
 
   describe "cookies" do