diff --git a/source/source_base/parallel_grid.cpp b/source/source_base/parallel_grid.cpp
index f213e800bb..86c7e90ace 100644
--- a/source/source_base/parallel_grid.cpp
+++ b/source/source_base/parallel_grid.cpp
@@ -94,7 +94,8 @@ void Parallel_Grid::init_parallel(const int nprocgroup)
         this->whichpro_loc[ip].assign(this->ncz, 0);
     }
 
-    this->z_distribution();
+    this->z_distribution(GlobalV::KPAR);
+
 }
 #endif
 void Parallel_Grid::init(const int& ncx_in,
@@ -107,18 +108,18 @@ void Parallel_Grid::init(const int& ncx_in,
                          const int nprocgroup)
 {
     this->init_serial(ncx_in, ncy_in, ncz_in, nczp_in, nrxx_in, nbz_in, bz_in);
-
 #ifdef __MPI
     this->init_parallel(nprocgroup);
 #endif
 }
-void Parallel_Grid::z_distribution()
+void Parallel_Grid::z_distribution(const int kpar)
 {
     assert(!this->numz.empty());
-
-    std::vector<int> startp(GlobalV::KPAR);
+    assert(kpar > 0);
+    
+    std::vector<int> startp(kpar);
     startp[0] = 0;
-    for (int ip = 0; ip < GlobalV::KPAR; ip++)
+    for (int ip = 0; ip < kpar; ip++)
     {
         const int nproc = nproc_in_pool[ip];
 
diff --git a/source/source_base/parallel_grid.h b/source/source_base/parallel_grid.h
index d8ad5e23c8..495021cc83 100644
--- a/source/source_base/parallel_grid.h
+++ b/source/source_base/parallel_grid.h
@@ -45,7 +45,7 @@ class Parallel_Grid
 
     private:
 
-    void z_distribution(void);
+    void z_distribution(const int kpar);
     
     void init_serial(const int& ncx_in,
                      const int& ncy_in,