diff --git a/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/evolution.h b/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/evolution.h
index b76d5e4aaaa..2089beb9a8c 100644
--- a/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/evolution.h
+++ b/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/evolution.h
@@ -123,7 +123,6 @@ public:
 #ifdef CGAL_OPTIMAL_BOUNDING_BOX_DEBUG
     std::cout << "offspringsA: \n" ;
     check_det(offspringsA);
-    std::cin.get();
 #endif
 
     // crossover II
diff --git a/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/optimal_bounding_box.h b/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/optimal_bounding_box.h
index 62017fc84d4..3cb4fc338a1 100644
--- a/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/optimal_bounding_box.h
+++ b/Optimal_bounding_box/include/CGAL/Optimal_bounding_box/optimal_bounding_box.h
@@ -200,7 +200,8 @@ void compute_optimal_bounding_box(const std::vector<Point>& points,
 #if defined(CGAL_EIGEN3_ENABLED)
   typedef CGAL::Eigen_linear_algebra_traits Linear_algebra_traits;
 #else
-  Linear_algebra_traits;
+  #pragma message("Error: You must either provide linear traits or link CGAL with the Eigen library")
+  Linear_algebra_traits; // no parameter provided, and Eigen is not enabled --> don't compile!
 #endif
 
   Linear_algebra_traits la_traits;
@@ -258,7 +259,8 @@ void compute_optimal_bounding_box(const PolygonMesh& pmesh,
 #if defined(CGAL_EIGEN3_ENABLED)
   typedef CGAL::Eigen_linear_algebra_traits Linear_algebra_traits;
 #else
-  Linear_algebra_traits;
+  #pragma message("Error: You must either provide linear traits or link CGAL with the Eigen library")
+  Linear_algebra_traits; // no parameter provided, and Eigen is not enabled --> don't compile!
 #endif
 
   Linear_algebra_traits la_traits;