diff --git a/daemon/fw/asf-measurements.hpp b/daemon/fw/asf-measurements.hpp
index a3eafc9..1d2b90f 100644
--- a/daemon/fw/asf-measurements.hpp
+++ b/daemon/fw/asf-measurements.hpp
@@ -105,8 +105,8 @@
   }
 
 public:
-  static const time::nanoseconds RTT_NO_MEASUREMENT;
-  static const time::nanoseconds RTT_TIMEOUT;
+  static constexpr time::nanoseconds RTT_NO_MEASUREMENT = -1_ns;
+  static constexpr time::nanoseconds RTT_TIMEOUT = -2_ns;
 
 private:
   ndn::util::RttEstimator m_rttEstimator;