diff --git a/rib/nrd.cpp b/rib/nrd.cpp
index be1f527..b4ff276 100644
--- a/rib/nrd.cpp
+++ b/rib/nrd.cpp
@@ -52,6 +52,13 @@
 {
 }
 
+Nrd::~Nrd()
+{
+  // It is necessary to explicitly define the destructor, because some member variables
+  // (e.g., unique_ptr<RibManager>) are forward-declared, but implicitly declared destructor
+  // requires complete types for all members when instantiated.
+}
+
 void
 Nrd::initialize()
 {