diff --git a/httparty.gemspec b/httparty.gemspec
index 8c579f4..4cfdcac 100644
--- a/httparty.gemspec
+++ b/httparty.gemspec
@@ -16,6 +16,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version     = '>= 2.0.0'
 
   s.add_dependency 'multi_xml', ">= 0.5.2"
+  s.add_dependency('mime-types', "~> 3.0")
 
   # If this line is removed, all hard partying will cease.
   s.post_install_message = "When you HTTParty, you must party hard!"
diff --git a/lib/httparty.rb b/lib/httparty.rb
index 167d93f..f2ffcb5 100644
--- a/lib/httparty.rb
+++ b/lib/httparty.rb
@@ -4,6 +4,7 @@ require 'net/https'
 require 'uri'
 require 'zlib'
 require 'multi_xml'
+require 'mime/types'
 require 'json'
 require 'csv'
 
diff --git a/lib/httparty/request/body.rb b/lib/httparty/request/body.rb
index 64892c9..c8637a7 100644
--- a/lib/httparty/request/body.rb
+++ b/lib/httparty/request/body.rb
@@ -35,9 +35,9 @@ module HTTParty
           memo += %(Content-Disposition: form-data; name="#{key}")
           # value.path is used to support ActionDispatch::Http::UploadedFile
           # https://github.com/jnunemaker/httparty/pull/585
-          memo += %(; filename="#{determine_file_name(value)}") if file?(value)
+          memo += %(; filename="#{file_name(value)}") if file?(value)
           memo += "\r\n"
-          memo += "Content-Type: application/octet-stream\r\n" if file?(value)
+          memo += "Content-Type: #{content_type(value)}\r\n" if file?(value)
           memo += "\r\n"
           memo += file?(value) ? value.read : value.to_s
           memo += "\r\n"
@@ -74,7 +74,13 @@ module HTTParty
         end
       end
 
-      def determine_file_name(object)
+      def content_type(object)
+        return object.content_type if object.respond_to?(:content_type)
+        mime = MIME::Types.type_for(file_name(object))
+        mime.empty? ? 'application/octet-stream' : mime[0].content_type
+      end
+
+      def file_name(object)
         object.respond_to?(:original_filename) ? object.original_filename : File.basename(object.path)
       end
 
diff --git a/spec/httparty/request/body_spec.rb b/spec/httparty/request/body_spec.rb
index f2e8faf..2a6470b 100644
--- a/spec/httparty/request/body_spec.rb
+++ b/spec/httparty/request/body_spec.rb
@@ -38,7 +38,7 @@ RSpec.describe HTTParty::Request::Body do
         end
         let(:expected_file_name) { 'tiny.gif' }
         let(:expected_file_contents) { "GIF89a\u0001\u0000\u0001\u0000\u0000\xFF\u0000,\u0000\u0000\u0000\u0000\u0001\u0000\u0001\u0000\u0000\u0002\u0000;" }
-        let(:expected_content_type) { 'application/octet-stream' }
+        let(:expected_content_type) { 'image/gif' }
         let(:multipart_params) do
           "--------------------------c772861a5109d5ef\r\n" \
           "Content-Disposition: form-data; name=\"user[avatar]\"; filename=\"#{expected_file_name}\"\r\n" \