diff --git a/4-GPU/HandsOn/.master/C/task5/poisson2d.solution.c b/4-GPU/HandsOn/.master/C/task5/poisson2d.solution.c
index 97fa97a756d602d226c8375cb81526099a506917..c91e21841b1c73fe6209c7980a9ab5ab3ef35fca 100644
--- a/4-GPU/HandsOn/.master/C/task5/poisson2d.solution.c
+++ b/4-GPU/HandsOn/.master/C/task5/poisson2d.solution.c
@@ -147,6 +147,8 @@ int main(int argc, char **argv) {
             }
         }
 
+#pragma acc wait
+
         real globalerror = 0.0;
         MPI_Allreduce(&error, &globalerror, 1, MPI_REAL_TYPE, MPI_MAX, MPI_COMM_WORLD);
         error = globalerror;
diff --git a/4-GPU/HandsOn/.master/C/task6/poisson2d.solution.c b/4-GPU/HandsOn/.master/C/task6/poisson2d.solution.c
index 5556ba3a914288c3d6f9e079ad1a8572b537cd6e..bf27e40780ccaa9824557e832b1209b3b6e9fbaa 100644
--- a/4-GPU/HandsOn/.master/C/task6/poisson2d.solution.c
+++ b/4-GPU/HandsOn/.master/C/task6/poisson2d.solution.c
@@ -167,6 +167,7 @@ int main(int argc, char **argv) {
                 error = fmaxr(error, fabsr(Anew[iy * nx + ix] - A[iy * nx + ix]));
             }
         }
+#pragma acc wait
 
         real globalerror = 0.0;
         MPI_Allreduce(&error, &globalerror, 1, MPI_REAL_TYPE, MPI_MAX, MPI_COMM_WORLD);
diff --git a/4-GPU/HandsOn/Solution/C/task5/poisson2d.solution.c b/4-GPU/HandsOn/Solution/C/task5/poisson2d.solution.c
index 97fa97a756d602d226c8375cb81526099a506917..c91e21841b1c73fe6209c7980a9ab5ab3ef35fca 100644
--- a/4-GPU/HandsOn/Solution/C/task5/poisson2d.solution.c
+++ b/4-GPU/HandsOn/Solution/C/task5/poisson2d.solution.c
@@ -147,6 +147,8 @@ int main(int argc, char **argv) {
             }
         }
 
+#pragma acc wait
+
         real globalerror = 0.0;
         MPI_Allreduce(&error, &globalerror, 1, MPI_REAL_TYPE, MPI_MAX, MPI_COMM_WORLD);
         error = globalerror;
diff --git a/4-GPU/HandsOn/Solution/C/task6/poisson2d.solution.c b/4-GPU/HandsOn/Solution/C/task6/poisson2d.solution.c
index 5556ba3a914288c3d6f9e079ad1a8572b537cd6e..bf27e40780ccaa9824557e832b1209b3b6e9fbaa 100644
--- a/4-GPU/HandsOn/Solution/C/task6/poisson2d.solution.c
+++ b/4-GPU/HandsOn/Solution/C/task6/poisson2d.solution.c
@@ -167,6 +167,7 @@ int main(int argc, char **argv) {
                 error = fmaxr(error, fabsr(Anew[iy * nx + ix] - A[iy * nx + ix]));
             }
         }
+#pragma acc wait
 
         real globalerror = 0.0;
         MPI_Allreduce(&error, &globalerror, 1, MPI_REAL_TYPE, MPI_MAX, MPI_COMM_WORLD);