diff --git a/libsrc/csg/python_csg.cpp b/libsrc/csg/python_csg.cpp
index b390fe7f..ec8759b6 100644
--- a/libsrc/csg/python_csg.cpp
+++ b/libsrc/csg/python_csg.cpp
@@ -642,7 +642,7 @@ However, when r = 0, the top part becomes a point(tip) and meshing fails!
                  cout << "Caught NgException: " << ex.What() << endl;
                }
              return dummy;
-           }))
+           }),py::call_guard<py::gil_scoped_release>())
     ;
 
   m.def("Save", FunctionPointer 
@@ -658,7 +658,7 @@ However, when r = 0, the top part becomes a point(tip) and meshing fails!
              *outfile << endl << endl << "endmesh" << endl << endl;
              geom.SaveToMeshFile (*outfile);
              delete outfile;
-           }))
+           }),py::call_guard<py::gil_scoped_release>())
     ;
 
 
@@ -669,7 +669,7 @@ However, when r = 0, the top part becomes a point(tip) and meshing fails!
             ZRefinementOptions opt;
             opt.minref = 5;
             ZRefinement (mesh, &geom, opt);
-          }))
+          }),py::call_guard<py::gil_scoped_release>())
     ;
 }
 
diff --git a/libsrc/meshing/python_mesh.cpp b/libsrc/meshing/python_mesh.cpp
index f549981c..f12600e0 100644
--- a/libsrc/meshing/python_mesh.cpp
+++ b/libsrc/meshing/python_mesh.cpp
@@ -540,9 +540,9 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
 	      ng_geometry = make_shared<NetgenGeometry>();
 	    self.SetGeometry(ng_geometry);
 	    delete infile;
-	  }))
+	  }),py::call_guard<py::gil_scoped_release>())
     // static_cast<void(Mesh::*)(const string & name)>(&Mesh::Load))
-    .def("Save", static_cast<void(Mesh::*)(const string & name)const>(&Mesh::Save))
+    .def("Save", static_cast<void(Mesh::*)(const string & name)const>(&Mesh::Save),py::call_guard<py::gil_scoped_release>())
     .def("Export",
          [] (Mesh & self, string filename, string format)
           {
@@ -557,7 +557,7 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
                 throw NgException (err);
               }
           },
-         py::arg("filename"), py::arg("format"))
+         py::arg("filename"), py::arg("format"),py::call_guard<py::gil_scoped_release>())
     
     .def_property("dim", &Mesh::GetDimension, &Mesh::SetDimension)
 
@@ -634,7 +634,7 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
     .def ("Compress", FunctionPointer ([](Mesh & self)
                                        {
                                          return self.Compress ();
-                                       }))
+                                       }),py::call_guard<py::gil_scoped_release>())
     
     
     .def ("SetBCName", &Mesh::SetBCName)
@@ -674,16 +674,19 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
              cout << "generate vol mesh" << endl;
 
              MeshingParameters mp;
+             {
+               py::gil_scoped_acquire acquire;
              if (py::extract<MeshingParameters>(pymp).check())
                mp = py::extract<MeshingParameters>(pymp)();
              else
                {
                  mp.optsteps3d = 5;
                }
+             }
              MeshVolume (mp, self);
              OptimizeVolume (mp, self);
            },
-          py::arg("mp")=NGDummyArgument())
+          py::arg("mp")=NGDummyArgument(),py::call_guard<py::gil_scoped_release>())
 
    .def ("OptimizeVolumeMesh", FunctionPointer
          ([](Mesh & self)
@@ -691,7 +694,7 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
             MeshingParameters mp;
             mp.optsteps3d = 5;
             OptimizeVolume (mp, self);
-          }))
+          }),py::call_guard<py::gil_scoped_release>())
 
     .def ("Refine", FunctionPointer
           ([](Mesh & self)
@@ -700,7 +703,7 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
                self.GetGeometry()->GetRefinement().Refine(self);
              else
                Refinement().Refine(self);
-           }))
+           }),py::call_guard<py::gil_scoped_release>())
 
     .def ("SecondOrder", FunctionPointer
           ([](Mesh & self)
@@ -725,7 +728,7 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
            }))
     */
     
-    .def ("BuildSearchTree", &Mesh::BuildElementSearchTree)
+    .def ("BuildSearchTree", &Mesh::BuildElementSearchTree,py::call_guard<py::gil_scoped_release>())
 
     .def ("BoundaryLayer", FunctionPointer 
           ([](Mesh & self, int bc, py::list thicknesses, int volnr, py::list materials)
diff --git a/libsrc/occ/python_occ.cpp b/libsrc/occ/python_occ.cpp
index 34df71c0..2c791639 100644
--- a/libsrc/occ/python_occ.cpp
+++ b/libsrc/occ/python_occ.cpp
@@ -29,7 +29,7 @@ DLL_HEADER void ExportNgOCC(py::module &m)
 
            self.HealGeometry();
            self.BuildFMap();
-         },py::arg("tolerance")=1e-3, py::arg("fixsmalledges")=true, py::arg("fixspotstripfaces")=true, py::arg("sewfaces")=true, py::arg("makesolids")=true, py::arg("splitpartitions")=false,R"raw_string(Heal the OCCGeometry.)raw_string")
+         },py::arg("tolerance")=1e-3, py::arg("fixsmalledges")=true, py::arg("fixspotstripfaces")=true, py::arg("sewfaces")=true, py::arg("makesolids")=true, py::arg("splitpartitions")=false,R"raw_string(Heal the OCCGeometry.)raw_string",py::call_guard<py::gil_scoped_release>())
       ;
     m.def("LoadOCCGeometry",FunctionPointer([] (const string & filename)
            {
@@ -38,7 +38,7 @@ DLL_HEADER void ExportNgOCC(py::module &m)
              OCCGeometry * instance = new OCCGeometry();
              instance = LoadOCC_STEP(filename.c_str());
              return shared_ptr<OCCGeometry>(instance, NOOP_Deleter);
-           }));
+           }),py::call_guard<py::gil_scoped_release>());
   m.def("GenerateMesh", FunctionPointer([] (shared_ptr<OCCGeometry> geo, MeshingParameters &param)
 					{
 					  auto mesh = make_shared<Mesh>();
@@ -55,7 +55,7 @@ DLL_HEADER void ExportNgOCC(py::module &m)
 					      cout << "Caught NgException: " << ex.What() << endl;
 					    }
 					  return mesh;
-					}))
+					}),py::call_guard<py::gil_scoped_release>())
     ;
 }
 
diff --git a/libsrc/stlgeom/python_stl.cpp b/libsrc/stlgeom/python_stl.cpp
index 37d3e1fc..bbb923a9 100644
--- a/libsrc/stlgeom/python_stl.cpp
+++ b/libsrc/stlgeom/python_stl.cpp
@@ -25,7 +25,7 @@ DLL_HEADER void ExportSTL(py::module & m)
 					   {
 					     ifstream ist(filename);
 					     return shared_ptr<STLGeometry>(STLGeometry::Load(ist));
-					   }));
+					   }),py::call_guard<py::gil_scoped_release>());
   m.def("GenerateMesh", FunctionPointer([] (shared_ptr<STLGeometry> geo, MeshingParameters &param)
 					{
 					  auto mesh = make_shared<Mesh>();
@@ -41,7 +41,7 @@ DLL_HEADER void ExportSTL(py::module & m)
 					      cout << "Caught NgException: " << ex.What() << endl;
 					    }
 					  return mesh;
-					}))
+					}),py::call_guard<py::gil_scoped_release>())
     ;
 }