diff --git a/src/mako/api/lib/mbuild.mako b/src/mako/api/lib/mbuild.mako
index c3a9a75bf7..cd35cb2fc9 100644
--- a/src/mako/api/lib/mbuild.mako
+++ b/src/mako/api/lib/mbuild.mako
@@ -738,9 +738,9 @@ else {
                         mp_reader.add_part(&mut request_value_reader, request_size, json_mime_type.clone())
                                  .add_part(&mut reader, size, reader_mime_type.clone());
                         let mime_type = mp_reader.mime_type();
-                        (&mut mp_reader as &mut dyn io::Read, (CONTENT_TYPE, mime_type.to_string()))
+                        (&mut mp_reader as &mut (dyn io::Read + Send), (CONTENT_TYPE, mime_type.to_string()))
                     },
-                    _ => (&mut request_value_reader as &mut dyn io::Read, (CONTENT_TYPE, json_mime_type.to_string())),
+                    _ => (&mut request_value_reader as &mut (dyn io::Read + Send), (CONTENT_TYPE, json_mime_type.to_string())),
                 };
             % endif
                 let client = &self.hub.client;
diff --git a/src/rust/api/client.rs b/src/rust/api/client.rs
index c1ee5ffd81..a1c3e4f762 100644
--- a/src/rust/api/client.rs
+++ b/src/rust/api/client.rs
@@ -360,8 +360,8 @@ const BOUNDARY: &str = "MDuXWGyeE33QFXGchb2VFWc4Z7945d";
 /// to google APIs, and might not be a fully-featured implementation.
 #[derive(Default)]
 pub struct MultiPartReader<'a> {
-    raw_parts: Vec<(HeaderMap, &'a mut dyn Read)>,
-    current_part: Option<(Cursor<Vec<u8>>, &'a mut dyn Read)>,
+    raw_parts: Vec<(HeaderMap, &'a mut (dyn Read + Send))>,
+    current_part: Option<(Cursor<Vec<u8>>, &'a mut (dyn Read + Send))>,
     last_part_boundary: Option<Cursor<Vec<u8>>>,
 }
 
@@ -384,7 +384,7 @@ impl<'a> MultiPartReader<'a> {
     /// `mime`    - It will be put onto the content type
     pub fn add_part(
         &mut self,
-        reader: &'a mut dyn Read,
+        reader: &'a mut (dyn Read + Send),
         size: u64,
         mime_type: Mime,
     ) -> &mut MultiPartReader<'a> {