diff --git a/src/util/lp/factorization.h b/src/util/lp/factorization.h
index 58ed176d0..408de84dd 100644
--- a/src/util/lp/factorization.h
+++ b/src/util/lp/factorization.h
@@ -104,7 +104,7 @@ struct const_iterator_mon {
 };
 
 struct factorization_factory {
-    const svector<lpvar>  m_vars;
+    const svector<lpvar>&  m_vars;
     const monomial*       m_monomial;
     // returns true if found
     virtual bool find_rm_monomial_of_vars(const svector<lpvar>& vars, unsigned& i) const = 0;