diff --git a/src/cut/sdpcuts/CouenneMatrix.hpp b/src/cut/sdpcuts/CouenneMatrix.hpp

index 38e1b8e..11e5365 100644

--- a/src/cut/sdpcuts/CouenneMatrix.hpp

+++ b/src/cut/sdpcuts/CouenneMatrix.hpp

@@ -69,7 +69,7 @@ namespace Couenne {

     struct compare_scalars {

       inline bool operator() (register CouenneScalar * const &a, 

-			      register CouenneScalar * const &b)

+			      register CouenneScalar * const &b) const

       {return a -> getIndex () < b -> getIndex ();}

     };