diff --git a/model/fw/per-fib-limits.h b/model/fw/per-fib-limits.h
index 3f23992..298c9ee 100644
--- a/model/fw/per-fib-limits.h
+++ b/model/fw/per-fib-limits.h
@@ -68,6 +68,11 @@
   WillSatisfyPendingInterest (Ptr<Face> inFace,
                               Ptr<pit::Entry> pitEntry);
 
+  virtual void
+  DidReceiveValidNack (Ptr<Face> inFace,
+                       uint32_t nackCode,
+                       Ptr<pit::Entry> pitEntry);
+  
 private:
   void
   ProcessFromQueue ();