diff --git a/candle-examples/examples/yolo-v3/darknet.rs b/candle-examples/examples/yolo-v3/darknet.rs
index 0c81bca8ef..6702618ec2 100644
--- a/candle-examples/examples/yolo-v3/darknet.rs
+++ b/candle-examples/examples/yolo-v3/darknet.rs
@@ -108,7 +108,7 @@ pub fn parse_config<T: AsRef<Path>>(path: T) -> Result<Darknet> {
 }
 
 enum Bl {
-    Layer(Box<dyn candle_nn::Module + Send>),
+    Layer(Box<dyn candle_nn::Module + Send + Sync>),
     Route(Vec<usize>),
     Shortcut(usize),
     Yolo(usize, Vec<(usize, usize)>),
diff --git a/candle-nn/src/func.rs b/candle-nn/src/func.rs
index e7fd73ae1d..39311d458c 100644
--- a/candle-nn/src/func.rs
+++ b/candle-nn/src/func.rs
@@ -1,10 +1,12 @@
 //! Layers defined by closures.
 use candle::{Result, Tensor};
+use std::sync::Arc;
 
 /// A layer defined by a simple closure.
+#[derive(Clone)]
 pub struct Func<'a> {
     #[allow(clippy::type_complexity)]
-    f: Box<dyn 'a + Fn(&Tensor) -> Result<Tensor> + Send>,
+    f: Arc<dyn 'a + Fn(&Tensor) -> Result<Tensor> + Send + Sync>,
 }
 
 impl<'a> std::fmt::Debug for Func<'a> {
@@ -15,9 +17,9 @@ impl<'a> std::fmt::Debug for Func<'a> {
 
 pub fn func<'a, F>(f: F) -> Func<'a>
 where
-    F: 'a + Fn(&Tensor) -> Result<Tensor> + Send,
+    F: 'a + Fn(&Tensor) -> Result<Tensor> + Send + Sync,
 {
-    Func { f: Box::new(f) }
+    Func { f: Arc::new(f) }
 }
 
 impl<'a> super::Module for Func<'a> {
@@ -29,8 +31,8 @@ impl<'a> super::Module for Func<'a> {
 impl<'a> Func<'a> {
     pub fn new<F>(f: F) -> Self
     where
-        F: 'a + Fn(&Tensor) -> Result<Tensor> + Send,
+        F: 'a + Fn(&Tensor) -> Result<Tensor> + Send + Sync,
     {
-        Self { f: Box::new(f) }
+        Self { f: Arc::new(f) }
     }
 }
diff --git a/candle-nn/src/sequential.rs b/candle-nn/src/sequential.rs
index 2fef774297..bef9975287 100644
--- a/candle-nn/src/sequential.rs
+++ b/candle-nn/src/sequential.rs
@@ -44,7 +44,7 @@ impl Sequential {
     /// Appends a closure after all the current layers.
     pub fn add_fn<F>(self, f: F) -> Self
     where
-        F: 'static + Fn(&Tensor) -> Result<Tensor> + Send,
+        F: 'static + Fn(&Tensor) -> Result<Tensor> + Send + Sync,
     {
         self.add(super::func(f))
     }