diff --git a/src/net/http/request.go b/src/net/http/request.go
index 4d01ed04b6..26da7adc25 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -411,7 +411,7 @@ var multipartByReader = &multipart.Form{
 }
 
 // MultipartReader returns a MIME multipart reader if this is a
-// multipart/form-data POST request, else returns nil and an error.
+// multipart/form-data or a multipart/mixed POST request, else returns nil and an error.
 // Use this function instead of ParseMultipartForm to
 // process the request body as a stream.
 func (r *Request) MultipartReader() (*multipart.Reader, error) {
@@ -422,16 +422,16 @@ func (r *Request) MultipartReader() (*multipart.Reader, error) {
 		return nil, errors.New("http: multipart handled by ParseMultipartForm")
 	}
 	r.MultipartForm = multipartByReader
-	return r.multipartReader()
+	return r.multipartReader(true)
 }
 
-func (r *Request) multipartReader() (*multipart.Reader, error) {
+func (r *Request) multipartReader(allowMixed bool) (*multipart.Reader, error) {
 	v := r.Header.Get("Content-Type")
 	if v == "" {
 		return nil, ErrNotMultipart
 	}
 	d, params, err := mime.ParseMediaType(v)
-	if err != nil || d != "multipart/form-data" {
+	if err != nil || d != "multipart/form-data" || (allowMixed && d != "multipart/mixed") {
 		return nil, ErrNotMultipart
 	}
 	boundary, ok := params["boundary"]
@@ -1207,7 +1207,7 @@ func (r *Request) ParseMultipartForm(maxMemory int64) error {
 		return nil
 	}
 
-	mr, err := r.multipartReader()
+	mr, err := r.multipartReader(false)
 	if err != nil {
 		return err
 	}