diff --git a/libsrc/general/mpi_interface.hpp b/libsrc/general/mpi_interface.hpp
index 593d290a..eb79865e 100644
--- a/libsrc/general/mpi_interface.hpp
+++ b/libsrc/general/mpi_interface.hpp
@@ -23,7 +23,7 @@ namespace netgen
 #endif
 
   /** This is the "standard" communicator that will be used for netgen-objects. **/
-  extern MPI_Comm ng_comm;
+  extern DLL_HEADER MPI_Comm ng_comm;
 
 #ifdef PARALLEL
   inline int MyMPI_GetNTasks (MPI_Comm comm = ng_comm)
diff --git a/libsrc/include/nginterface.h b/libsrc/include/nginterface.h
index 254734ce..38e38ec2 100644
--- a/libsrc/include/nginterface.h
+++ b/libsrc/include/nginterface.h
@@ -40,7 +40,7 @@
 #ifndef PARALLEL
   typedef int MPI_Comm;
 #endif
-namespace netgen { extern MPI_Comm ng_comm; }
+namespace netgen { extern DLL_HEADER MPI_Comm ng_comm; }
 
 
 // implemented element types:
diff --git a/libsrc/include/nginterface_v2.hpp b/libsrc/include/nginterface_v2.hpp
index d731deaf..d6d4c5a8 100644
--- a/libsrc/include/nginterface_v2.hpp
+++ b/libsrc/include/nginterface_v2.hpp
@@ -29,7 +29,7 @@ enum NG_REFINEMENT_TYPE { NG_REFINE_H = 0, NG_REFINE_P = 1, NG_REFINE_HP = 2 };
 #ifndef PARALLEL
   typedef int MPI_Comm;
 #endif
-namespace netgen { extern MPI_Comm ng_comm; }
+namespace netgen { extern DLL_HEADER MPI_Comm ng_comm; }
 
 
 namespace netgen
diff --git a/libsrc/meshing/global.cpp b/libsrc/meshing/global.cpp
index 988dc8e6..327727be 100644
--- a/libsrc/meshing/global.cpp
+++ b/libsrc/meshing/global.cpp
@@ -32,7 +32,7 @@ namespace netgen
   // TraceGlobal glob2("global2");
 
   // global communicator for netgen
-  MPI_Comm ng_comm = MPI_COMM_WORLD;
+  DLL_HEADER MPI_Comm ng_comm = MPI_COMM_WORLD;
   
   weak_ptr<Mesh> global_mesh;
   void SetGlobalMesh (shared_ptr<Mesh> m)
diff --git a/libsrc/meshing/global.hpp b/libsrc/meshing/global.hpp
index 9b1bbac7..c97815e3 100644
--- a/libsrc/meshing/global.hpp
+++ b/libsrc/meshing/global.hpp
@@ -61,7 +61,7 @@ namespace netgen
   DLL_HEADER void SetGlobalMesh (shared_ptr<Mesh> m);
 
   // global communicator for netgen (dummy if no MPI)
-  extern MPI_Comm ng_comm;
+  extern DLL_HEADER MPI_Comm ng_comm;
   
 }