diff --git a/mex/sources/local_state_space_iterations/local_state_space_iteration_2.cc b/mex/sources/local_state_space_iterations/local_state_space_iteration_2.cc
index 8c81fdfbf67ba00cf7963ffbf16b31bb9bd5bd0a..abdb3e58bd925276284f7efc0e09cb488238e6c5 100644
--- a/mex/sources/local_state_space_iterations/local_state_space_iteration_2.cc
+++ b/mex/sources/local_state_space_iterations/local_state_space_iteration_2.cc
@@ -108,7 +108,7 @@ ss2Iteration_pruning(double *y2, double *y1, const double *yhat2, const double *
           // +ghxu·yhat1⊗u
           for (int v = particle__, i = 0; v < particle__+n; v++)
             for (int s = particle___; s < particle___+q; s++, i += m)
-              y2[variable_] += ghxu[variable+i]*epsilon[s]*yhat2[v];
+              y2[variable_] += ghxu[variable+i]*epsilon[s]*yhat1[v];
 #ifdef FIRST_ORDER_LOOP
           for (int column = 0, column_ = 0; column < q; column++, column_ += m)
             {