diff --git a/tools/peek/ndnpoke/ndnpoke.hpp b/tools/peek/ndnpoke/ndnpoke.hpp
index 16a3795..a3cd393 100644
--- a/tools/peek/ndnpoke/ndnpoke.hpp
+++ b/tools/peek/ndnpoke/ndnpoke.hpp
@@ -49,7 +49,7 @@
   // program behavior options
   bool isVerbose = false;
   bool wantUnsolicited = false;
-  optional<time::milliseconds> timeout;
+  std::optional<time::milliseconds> timeout;
 };
 
 class NdnPoke : noncopyable