diff --git a/rib/face-entry.hpp b/rib/face-entry.hpp
index 15a8aaf..bd3f1f9 100644
--- a/rib/face-entry.hpp
+++ b/rib/face-entry.hpp
@@ -66,6 +66,10 @@
   return (entry.faceId == faceId);
 }
 
+// Method definition in rib-entry.cpp
+std::ostream&
+operator<<(std::ostream& os, const FaceEntry& entry);
+
 } // namespace rib
 } // namespace nfd