diff --git a/src/main_gpumd/add_force.cu b/src/main_gpumd/add_force.cu
index cbf1a01b0..03f942fe5 100644
--- a/src/main_gpumd/add_force.cu
+++ b/src/main_gpumd/add_force.cu
@@ -55,7 +55,7 @@ void Add_Force::compute(const int step, const std::vector<Group>& groups, Atom&
     const int num_atoms_total = atom.force_per_atom.size() / 3;
     const int group_size = groups[grouping_method_[call]].cpu_size[group_id_[call]];
     const int group_size_sum = groups[grouping_method_[call]].cpu_size_sum[group_id_[call]];
-    add_force<<<(atom.number_of_atoms - 1) / 64 + 1, 64>>>(
+    add_force<<<(group_size - 1) / 64 + 1, 64>>>(
       group_size,
       group_size_sum,
       groups[grouping_method_[call]].contents.data(),
@@ -154,7 +154,9 @@ void Add_Force::parse(const char** param, int num_param, const std::vector<Group
 
   ++num_calls_;
 
-  exit(1);
+  if (num_calls_ > 10) {
+    PRINT_INPUT_ERROR("add_force cannot be used more than 10 times in one run.");
+  }
 }
 
 void Add_Force::finalize() 
diff --git a/src/main_gpumd/run.cu b/src/main_gpumd/run.cu
index 1928a023a..aea3b6c8b 100644
--- a/src/main_gpumd/run.cu
+++ b/src/main_gpumd/run.cu
@@ -466,7 +466,7 @@ void Run::parse_one_keyword(std::vector<std::string>& tokens)
     electron_stop.parse(param, num_param, atom.number_of_atoms, number_of_types);
   } else if (strcmp(param[0], "add_force") == 0) {
     add_force.parse(param, num_param, group);
-  }else if (strcmp(param[0], "mc") == 0) {
+  } else if (strcmp(param[0], "mc") == 0) {
     mc.parse_mc(param, num_param, group, atom);
   } else if (strcmp(param[0], "dftd3") == 0) {
     // nothing here; will be handled elsewhere