diff --git a/libsrc/csg/surface.hpp b/libsrc/csg/surface.hpp
index f09d8c51..7cd31b27 100644
--- a/libsrc/csg/surface.hpp
+++ b/libsrc/csg/surface.hpp
@@ -19,7 +19,7 @@ namespace netgen
      This class is used for generation of surface meshes
      in NETGEN 
   */
-  class Surface
+  class DLL_HEADER Surface
   {
   protected:
     /// invert normal vector
@@ -236,7 +236,7 @@ namespace netgen
 
 
 
-  class Primitive
+  class DLL_HEADER Primitive
   {
   protected:
     NgArray<int> surfaceids;
diff --git a/libsrc/stlgeom/stltopology.hpp b/libsrc/stlgeom/stltopology.hpp
index 101cde53..6f916bed 100644
--- a/libsrc/stlgeom/stltopology.hpp
+++ b/libsrc/stlgeom/stltopology.hpp
@@ -276,7 +276,7 @@ ostream& operator<<(ostream& os, const STLTriangle& t);
 
 
 
-class STLTopology
+class DLL_HEADER STLTopology
 {
 protected:
   Array<STLTriangle, STLTrigId> trias;