diff --git a/hellosign_sdk/utils/hsformat.py b/hellosign_sdk/utils/hsformat.py
index d110c1f..2508515 100644
--- a/hellosign_sdk/utils/hsformat.py
+++ b/hellosign_sdk/utils/hsformat.py
@@ -22,6 +22,7 @@
 # SOFTWARE.
 #
 
+import os
 
 class HSFormat(object):
     ''' Authentication object using HelloSign's access token '''
@@ -42,10 +43,13 @@ def format_file_params(files):
         '''
             Utility method for formatting file parameters for transmission
         '''
-        files_payload = {}
+        files_payload = []
         if files:
             for idx, filename in enumerate(files):
-                files_payload["file[" + str(idx) + "]"] = open(filename, 'rb')
+                files_payload.append((
+                    'file[%s]' % idx,
+                     (os.path.basename(filename), open(filename, 'rb'))
+                ))
         return files_payload
 
     @staticmethod
@@ -129,4 +133,4 @@ def format_custom_fields(list_of_custom_fields):
     @staticmethod
     def strip_none_values(dictionary):
         if dictionary:
-            return dict((key, value) for (key, value) in dictionary.items() if value)
\ No newline at end of file
+            return dict((key, value) for (key, value) in dictionary.items() if value)