diff --git a/codex-rs/core/src/model_visible_context.rs b/codex-rs/core/src/model_visible_context.rs
index 88335476f8..e96e078d32 100644
--- a/codex-rs/core/src/model_visible_context.rs
+++ b/codex-rs/core/src/model_visible_context.rs
@@ -69,9 +69,9 @@ pub(crate) trait ContextualUserFragment {
     }
 
     fn wrap_contextual_user_body(body: String) -> String {
-        let markers = Self::markers().expect(
-            "contextual-user fragments using wrap_contextual_user_body must define markers",
-        );
+        let Some(markers) = Self::markers() else {
+            panic!("contextual-user fragments using wrap_contextual_user_body must define markers");
+        };
         markers.wrap_body(body)
     }
 }