diff --git a/src/node/mac48-address.cc b/src/node/mac48-address.cc
index 998bb2b11..c71131342 100644
--- a/src/node/mac48-address.cc
+++ b/src/node/mac48-address.cc
@@ -95,7 +95,7 @@ Mac48Address::IsMatchingType (const Address &address)
 {
   return address.CheckCompatible (GetType (), 6);
 }
-Mac48Address::operator Address ()
+Mac48Address::operator Address () const
 {
   return ConvertTo ();
 }
diff --git a/src/node/mac48-address.h b/src/node/mac48-address.h
index 1a290dad3..a0649a5c2 100644
--- a/src/node/mac48-address.h
+++ b/src/node/mac48-address.h
@@ -61,7 +61,7 @@ public:
    *
    * Convert an instance of this class to a polymorphic Address instance.
    */
-  operator Address ();
+  operator Address () const;
   /**
    * \param address a polymorphic address
    * \returns a new Mac48Address from the polymorphic address