diff --git a/mitmproxy/net/http/multipart.py b/mitmproxy/net/http/multipart.py
index a854d47fd..4edf76acd 100644
--- a/mitmproxy/net/http/multipart.py
+++ b/mitmproxy/net/http/multipart.py
@@ -1,8 +1,43 @@
 import re
-
+import mimetypes
+from urllib.parse import quote
 from mitmproxy.net.http import headers
 
 
+def encode(head, l):
+
+    k = head.get("content-type")
+    if k:
+        k = headers.parse_content_type(k)
+        if k is not None:
+            try:
+                boundary = k[2]["boundary"].encode("ascii")
+                boundary = quote(boundary)
+            except (KeyError, UnicodeError):
+                return b""
+            hdrs = []
+            for key, value in l:
+                file_type = mimetypes.guess_type(str(key))[0] or "text/plain; charset=utf-8"
+
+                if key:
+                    hdrs.append(b"--%b" % boundary.encode('utf-8'))
+                    disposition = b'form-data; name="%b"' % key
+                    hdrs.append(b"Content-Disposition: %b" % disposition)
+                    hdrs.append(b"Content-Type: %b" % file_type.encode('utf-8'))
+                    hdrs.append(b'')
+                    hdrs.append(value)
+                hdrs.append(b'')
+
+                if value is not None:
+                    # If boundary is found in value then raise ValueError
+                    if re.search(rb"^--%b$" % re.escape(boundary.encode('utf-8')), value):
+                        raise ValueError(b"boundary found in encoded string")
+
+            hdrs.append(b"--%b--\r\n" % boundary.encode('utf-8'))
+            temp = b"\r\n".join(hdrs)
+            return temp
+
+
 def decode(hdrs, content):
     """
         Takes a multipart boundary encoded string and returns list of (key, value) tuples.
@@ -19,14 +54,14 @@ def decode(hdrs, content):
 
         rx = re.compile(br'\bname="([^"]+)"')
         r = []
-
-        for i in content.split(b"--" + boundary):
-            parts = i.splitlines()
-            if len(parts) > 1 and parts[0][0:2] != b"--":
-                match = rx.search(parts[1])
-                if match:
-                    key = match.group(1)
-                    value = b"".join(parts[3 + parts[2:].index(b""):])
-                    r.append((key, value))
+        if content is not None:
+            for i in content.split(b"--" + boundary):
+                parts = i.splitlines()
+                if len(parts) > 1 and parts[0][0:2] != b"--":
+                    match = rx.search(parts[1])
+                    if match:
+                        key = match.group(1)
+                        value = b"".join(parts[3 + parts[2:].index(b""):])
+                        r.append((key, value))
         return r
     return []
diff --git a/mitmproxy/net/http/request.py b/mitmproxy/net/http/request.py
index 218699e0d..783fd5ff4 100644
--- a/mitmproxy/net/http/request.py
+++ b/mitmproxy/net/http/request.py
@@ -468,8 +468,8 @@ class Request(message.Message):
         return ()
 
     def _set_multipart_form(self, value):
+        self.content = mitmproxy.net.http.multipart.encode(self.headers, value)
         self.headers["content-type"] = "multipart/form-data"
-        self.content = mitmproxy.net.http.url.encode(value, self.get_text(strict=False)).encode()
 
     @property
     def multipart_form(self):
diff --git a/test/mitmproxy/net/http/test_multipart.py b/test/mitmproxy/net/http/test_multipart.py
index 68ae6bbdf..ce7dee5a7 100644
--- a/test/mitmproxy/net/http/test_multipart.py
+++ b/test/mitmproxy/net/http/test_multipart.py
@@ -1,5 +1,6 @@
 from mitmproxy.net.http import Headers
 from mitmproxy.net.http import multipart
+import pytest
 
 
 def test_decode():
@@ -22,3 +23,20 @@ def test_decode():
     assert len(form) == 2
     assert form[0] == (b"field1", b"value1")
     assert form[1] == (b"field2", b"value2")
+
+
+def test_encode():
+    data = [("file".encode('utf-8'), "shell.jpg".encode('utf-8')),
+            ("file_size".encode('utf-8'), "1000".encode('utf-8'))]
+    headers = Headers(
+        content_type='multipart/form-data; boundary=127824672498'
+    )
+    content = multipart.encode(headers, data)
+
+    assert b'Content-Disposition: form-data; name="file"' in content
+    assert b'Content-Type: text/plain; charset=utf-8\r\n\r\nshell.jpg\r\n\r\n--127824672498\r\n' in content
+    assert b'1000\r\n\r\n--127824672498--\r\n'
+    assert len(content) == 252
+
+    with pytest.raises(ValueError, match=r"boundary found in encoded string"):
+        multipart.encode(headers, [("key".encode('utf-8'), "--127824672498".encode('utf-8'))])
diff --git a/test/mitmproxy/net/http/test_request.py b/test/mitmproxy/net/http/test_request.py
index 6ef73389b..71d5c7a12 100644
--- a/test/mitmproxy/net/http/test_request.py
+++ b/test/mitmproxy/net/http/test_request.py
@@ -371,7 +371,7 @@ class TestRequestUtils:
             assert list(request.multipart_form.items()) == []
 
     def test_set_multipart_form(self):
-        request = treq(content=b"foobar")
-        request.multipart_form = [("filename", "shell.jpg"), ("file_size", "1000")]
-        assert request.headers['Content-Type'] == "multipart/form-data"
-        assert request.content
+        request = treq()
+        request.multipart_form = [("file", "shell.jpg"), ("file_size", "1000")]
+        assert request.headers["Content-Type"] == 'multipart/form-data'
+        assert request.content is None