diff --git a/lib/restclient/payload.rb b/lib/restclient/payload.rb
index 56563fa5..027d0372 100644
--- a/lib/restclient/payload.rb
+++ b/lib/restclient/payload.rb
@@ -8,7 +8,9 @@ module RestClient
   module Payload
     extend self
 
-    def generate(params)
+    def generate(params, boundary=nil)
+      @boundary = boundary if boundary
+
       if params.is_a?(String)
         Base.new(params)
       elsif params.is_a?(Hash)
diff --git a/lib/restclient/request.rb b/lib/restclient/request.rb
index a875dc0b..e176156f 100644
--- a/lib/restclient/request.rb
+++ b/lib/restclient/request.rb
@@ -74,7 +74,7 @@ def initialize args
       # process cookie arguments found in headers or args
       @cookie_jar = process_cookie_args!(@uri, @headers, args)
 
-      @payload = Payload.generate(args[:payload])
+      @payload = Payload.generate(args[:payload], args[:boundary])
 
       @user = args[:user] if args.include?(:user)
       @password = args[:password] if args.include?(:password)