diff --git a/ctrl/app.py b/ctrl/app.py
index 2e8f297..d7b1be9 100644
--- a/ctrl/app.py
+++ b/ctrl/app.py
@@ -83,7 +83,7 @@ def api_capabilities():
         for w in wrk.probe_all()
         if w.get("os") and w.get("cpu")
     }
-    return jsonify(sorted({"os": o, "cpu": c} for o, c in combos if o and c))
+    return jsonify([{"os": o, "cpu": c} for o, c in sorted(combos)])
 
 
 @app.post("/api/jobs")