diff --git a/src/machine.rs b/src/machine.rs
index f6eac7e..5fae20c 100644
--- a/src/machine.rs
+++ b/src/machine.rs
@@ -31,8 +31,8 @@ pub struct Machine {
     #[cfg(feature = "bonus:heap")]
     pub heap: Heap,
 
-    pub stream_in: Box<Read + Send>,
-    pub stream_out: Rc<Mutex<Write + Send>>,
+    pub stream_in: Box<Read + Send + Sync>,
+    pub stream_out: Rc<Mutex<Write + Send + Sync>>,
 
 }
 
@@ -148,11 +148,11 @@ impl Machine {
         Ok(self.block.read_u8()? as usize)
     }
 
-    pub fn set_input(&mut self, instream: Box<Read + Send>) {
+    pub fn set_input(&mut self, instream: Box<Read + Send + Sync>) {
         self.stream_in = instream;
     }
 
-    pub fn set_output(&mut self, outstream: Rc<Mutex<Write + Send>>) {
+    pub fn set_output(&mut self, outstream: Rc<Mutex<Write + Send + Sync>>) {
         self.stream_out = outstream;
     }
 }
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