diff --git a/Solver_interface/include/CGAL/Eigen_vector.h b/Solver_interface/include/CGAL/Eigen_vector.h
index 6280e289be1..3e7c11501af 100644
--- a/Solver_interface/include/CGAL/Eigen_vector.h
+++ b/Solver_interface/include/CGAL/Eigen_vector.h
@@ -72,7 +72,7 @@ public:
 
    /// Return the vector's number of coefficients.
    int dimension() const {
-       return this->size();
+       return static_cast<int>(this->size());
    }
 
    /// Get vector wrapped by this object.