--- matrix_expression.hpp.orig	2008-05-01 11:11:57.690870000 +0100
+++ matrix_expression.hpp	2008-05-07 13:58:59.998389000 +0100
@@ -2940,7 +2940,9 @@ namespace boost { namespace numeric { na
     // (t * m) [i] [j] = t * m [i] [j]
     template<class T1, class E2>
     BOOST_UBLAS_INLINE
+    typename enable_if< is_convertible<T1, typename E2::value_type >,
     typename matrix_binary_scalar1_traits<const T1, E2, scalar_multiplies<T1, typename E2::value_type> >::result_type
+    >::type
     operator * (const T1 &e1,
                 const matrix_expression<E2> &e2) {
         typedef typename matrix_binary_scalar1_traits<const T1, E2, scalar_multiplies<T1, typename E2::value_type> >::expression_type expression_type;
@@ -3373,7 +3375,9 @@ namespace boost { namespace numeric { na
     // (m * t) [i] [j] = m [i] [j] * t
     template<class E1, class T2>
     BOOST_UBLAS_INLINE
+    typename enable_if< is_convertible<T2, typename E1::value_type>,
     typename matrix_binary_scalar2_traits<E1, const T2, scalar_multiplies<typename E1::value_type, T2> >::result_type
+    >::type
     operator * (const matrix_expression<E1> &e1,
                 const T2 &e2) {
         typedef typename matrix_binary_scalar2_traits<E1, const T2, scalar_multiplies<typename E1::value_type, T2> >::expression_type expression_type;