diff --git a/src/internet/test/error-channel.h b/src/internet/test/error-channel.h
index 961f60a50..92c39685d 100644
--- a/src/internet/test/error-channel.h
+++ b/src/internet/test/error-channel.h
@@ -44,7 +44,7 @@ public:
   virtual void Send (Ptr<Packet> p, uint16_t protocol, Mac48Address to, Mac48Address from,
                      Ptr<SimpleNetDevice> sender);
 
-  void Add (Ptr<SimpleNetDevice> device);
+  virtual void Add (Ptr<SimpleNetDevice> device);
 
   // inherited from ns3::Channel
   virtual uint32_t GetNDevices (void) const;
diff --git a/src/network/utils/simple-channel.h b/src/network/utils/simple-channel.h
index 7329a1de6..53649c82c 100644
--- a/src/network/utils/simple-channel.h
+++ b/src/network/utils/simple-channel.h
@@ -59,7 +59,7 @@ public:
    *
    * \param device the device to attach to the channel
    */ 
-  void Add (Ptr<SimpleNetDevice> device);
+  virtual void Add (Ptr<SimpleNetDevice> device);
 
   // inherited from ns3::Channel
   virtual uint32_t GetNDevices (void) const;