diff --git a/src/sing/jack.rs b/src/sing/jack.rs
index a833244..20f5c23 100644
--- a/src/sing/jack.rs
+++ b/src/sing/jack.rs
@@ -93,6 +93,20 @@ impl<'j> Jack<'j> {
     }
 }
 
-impl<'j> HasJack<'j> for Jack<'j> { fn jack (&self) -> &Jack<'j> { self } }
+impl<'j> HasJack<'j> for Jack<'j> {
+    fn jack (&self) -> &Jack<'j> {
+        self
+    }
+}
 
-impl<'j> HasJack<'j> for &Jack<'j> { fn jack (&self) -> &Jack<'j> { self } }
+impl<'j> HasJack<'j> for &Jack<'j> {
+    fn jack (&self) -> &Jack<'j> {
+        self
+    }
+}
+
+impl<'j, T: HasJack<'j>> HasJack<'j> for Arc<T> {
+    fn jack (&self) -> &Jack<'j> {
+        (&**self).jack()
+    }
+}