diff --git a/include/seastar/core/reactor.hh b/include/seastar/core/reactor.hh
index a16a81c604d..d3fd0c49b9a 100644
--- a/include/seastar/core/reactor.hh
+++ b/include/seastar/core/reactor.hh
@@ -219,7 +219,7 @@ public:
 private:
     std::shared_ptr<smp> _smp;
     alien::instance& _alien;
-    reactor_config _cfg;
+    const reactor_config _cfg;
     file_desc _notify_eventfd;
     file_desc _task_quota_timer;
 #ifdef HAVE_OSV