diff --git a/aiohttp/multipart.py b/aiohttp/multipart.py
index 47caad26d49..079b9e935d0 100644
--- a/aiohttp/multipart.py
+++ b/aiohttp/multipart.py
@@ -655,6 +655,7 @@ def __init__(self, obj, headers=None, *, chunk_size=8192):
         self._serialize_map = {
             bytes: self._serialize_bytes,
             str: self._serialize_str,
+            int: self._serialize_int,
             io.IOBase: self._serialize_io,
             MultipartWriter: self._serialize_multipart,
             ('application', 'json'): self._serialize_json,
@@ -757,6 +758,9 @@ def _serialize_str(self, obj):
         *_, params = parse_mimetype(self.headers.get(CONTENT_TYPE))
         yield obj.encode(params.get('charset', 'us-ascii'))
 
+    def _serialize_int(self, obj):
+        return self._serialize_str(str(obj))
+
     def _serialize_io(self, obj):
         while True:
             chunk = obj.read(self._chunk_size)
diff --git a/tests/test_multipart.py b/tests/test_multipart.py
index cb39656ad4d..ae1e1811e3b 100644
--- a/tests/test_multipart.py
+++ b/tests/test_multipart.py
@@ -772,6 +772,9 @@ def test_serialize_bytes(self):
     def test_serialize_str(self):
         self.assertEqual(b'foo', next(self.part._serialize_str('foo')))
 
+    def test_serialize_int(self):
+        self.assertEqual(b'42', next(self.part._serialize_int(42)))
+
     def test_serialize_str_custom_encoding(self):
         self.part.headers[CONTENT_TYPE] = \
             'text/plain;charset=cp1251'