diff --git a/server/src/main.rs b/server/src/main.rs
index fdec14a..b2876d7 100644
--- a/server/src/main.rs
+++ b/server/src/main.rs
@@ -200,7 +200,9 @@ mod infra_axum_handlers {
         )
     }
 
-    pub fn handle_get_metrics(State(state): State<SharedAppState>) -> () {
+    pub fn handle_get_metrics(
+        State(state): State<SharedAppState>,
+    ) -> impl Handler<_, SharedAppState, ()> {
         // we need a separate handler function to create an error tracing span
         #[tracing::instrument]
         async fn handler(state: &SharedAppState) -> Response {