--- a/src/core/random-variable.cc	Wed Feb 20 20:24:52 2008 +0100
+++ b/src/core/random-variable.cc	Wed Feb 20 20:57:59 2008 +0100
@@ -309,7 +309,7 @@
   return ClassValueHelperConvertTo<RandomVariable,RandomVariableValue> (this);
 }
 
-Ptr<AttributeChecker> 
+Ptr<const AttributeChecker> 
 MakeRandomVariableChecker (void)
 {
   return MakeSimpleAttributeChecker<RandomVariableValue> ();