diff --git a/core/include/engine/Solver_Heun.hpp b/core/include/engine/Solver_Heun.hpp
index 4cb85d2f0..d72820c60 100644
--- a/core/include/engine/Solver_Heun.hpp
+++ b/core/include/engine/Solver_Heun.hpp
@@ -65,7 +65,7 @@ void Method_Solver<Solver::Heun>::Iteration ()
         // Second step - Corrector
         Backend::par::apply( nos, [conf, conf_predictor, f_virtual, f_virtual_predictor] SPIRIT_LAMBDA (int idx) {
             conf[idx] = (
-                conf[idx] + 0.5*( conf[idx] - 0.5*conf[idx].cross(f_virtual[idx]) - conf_predictor[idx].cross(f_virtual_predictor[idx]) )
+                conf[idx] - 0.5 * ( conf[idx].cross( f_virtual[idx] ) + conf_predictor[idx].cross(f_virtual_predictor[idx]) )
             ).normalized();
         } );
     }
diff --git a/core/include/engine/Solver_SIB.hpp b/core/include/engine/Solver_SIB.hpp
index 179f4d4ca..e79be815d 100644
--- a/core/include/engine/Solver_SIB.hpp
+++ b/core/include/engine/Solver_SIB.hpp
@@ -30,8 +30,8 @@ void Method_Solver<Solver::SIB>::Iteration ()
     this->Calculate_Force_Virtual(this->configurations, this->forces, this->forces_virtual);
     for (int i = 0; i < this->noi; ++i)
     {
-        auto image      = *this->systems[i]->spins;
-        auto predictor  = *this->configurations_predictor[i];
+        auto& image     = *this->systems[i]->spins;
+        auto& predictor = *this->configurations_predictor[i];
         Solver_Kernels::sib_transform(image, forces_virtual[i], predictor);
 
         auto imagep     = this->systems[i]->spins->data();