diff --git a/multipart/multipart.py b/multipart/multipart.py
index 170151f..2c26b62 100644
--- a/multipart/multipart.py
+++ b/multipart/multipart.py
@@ -1937,6 +1937,10 @@ def parse_form(
         content_length = float("inf")
     bytes_read = 0
 
+    # If the input stream is a text stream, use its binary buffer
+    if isinstance (input_stream, io .TextIOBase):
+        input_stream = input_stream .buffer
+
     while True:
         # Read only up to the Content-Length given.
         max_readable = min(content_length - bytes_read, 1048576)
diff --git a/tests/test_multipart.py b/tests/test_multipart.py
index 3a814fb..6df98a2 100644
--- a/tests/test_multipart.py
+++ b/tests/test_multipart.py
@@ -5,7 +5,7 @@
 import sys
 import tempfile
 import unittest
-from io import BytesIO
+from io import BytesIO, TextIOBase
 from typing import TYPE_CHECKING
 from unittest.mock import Mock
 
@@ -1268,7 +1268,7 @@ def test_create_form_parser_error(self):
         with self.assertRaises(ValueError):
             create_form_parser(headers, None, None)
 
-    def test_parse_form(self):
+    def test_parse_form_bytes(self):
         on_field = Mock()
         on_file = Mock()
 
@@ -1280,6 +1280,37 @@ def test_parse_form(self):
         # 15 - i.e. all data is written.
         self.assertEqual(on_file.call_args[0][0].size, 15)
 
+    def test_parse_form_file(self):
+        on_field = Mock()
+        on_file = Mock()
+
+        with open ('12345678.txt', 'wt+') as f:
+            f .write ('123456789012345')
+            f .seek (0o0)
+            parse_form({"Content-Type": "application/octet-stream"}, f .buffer, on_field, on_file)
+
+        assert on_file.call_count == 1
+
+        # Assert that the first argument of the call (a File object) has size
+        # 15 - i.e. all data is written.
+        self.assertEqual(on_file.call_args[0][0].size, 15)
+
+    def test_parse_form_text(self):
+        on_field = Mock()
+        on_file = Mock()
+
+        with open ('12345678.txt', 'wt+') as f:
+            f .write ('123456789012345')
+            f .seek (0o0)
+            self .assertTrue (isinstance (f, TextIOBase))
+            parse_form({"Content-Type": "application/octet-stream"}, f, on_field, on_file)
+
+        assert on_file.call_count == 1
+
+        # Assert that the first argument of the call (a File object) has size
+        # 15 - i.e. all data is written.
+        self.assertEqual(on_file.call_args[0][0].size, 15)
+
     def test_parse_form_content_length(self):
         files = []