diff --git a/src/data.hpp b/src/data.hpp
index 70d1a72..1480103 100644
--- a/src/data.hpp
+++ b/src/data.hpp
@@ -321,6 +321,8 @@
   friend class nfd::LocalControlHeader;
 };
 
+std::ostream&
+operator<<(std::ostream& os, const Data& data);
 
 inline bool
 Data::hasWire() const
diff --git a/src/interest.cpp b/src/interest.cpp
index 986a5ec..a6bd107 100644
--- a/src/interest.cpp
+++ b/src/interest.cpp
@@ -255,7 +255,7 @@
   }
   if (interest.getInterestLifetime() >= time::milliseconds::zero()
       && interest.getInterestLifetime() != DEFAULT_INTEREST_LIFETIME) {
-    os << delim << "ndn.InterestLifetime=" << interest.getInterestLifetime();
+    os << delim << "ndn.InterestLifetime=" << interest.getInterestLifetime().count();
     delim = '&';
   }