diff --git a/src/server.rs b/src/server.rs
index 853d39e34..36b25ff24 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -179,8 +179,7 @@ impl<State: Clone + Send + Sync + 'static> Server<State> {
         M: Middleware<State>,
     {
         log::trace!("Adding middleware {}", middleware.name());
-        let m = Arc::get_mut(&mut self.middleware)
-            .expect("Registering middleware is not possible after the Server has started");
+        let m = Arc::make_mut(&mut self.middleware);
         m.push(Arc::new(middleware));
         self
     }