diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 60cb64b7b..6ea8a6cc8 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -1025,6 +1025,7 @@ void processConnection(
 {
 #ifndef _WIN32 // TODO need graceful async exit support on Windows?
     auto monitor = !recursive ? std::make_unique<MonitorFdHup>(from.fd) : nullptr;
+    (void) monitor; // suppress warning
 #endif
 
     /* Exchange the greeting. */