diff --git a/libsrc/csg/csgeom.hpp b/libsrc/csg/csgeom.hpp
index 40d90d51..dc5a4d4f 100644
--- a/libsrc/csg/csgeom.hpp
+++ b/libsrc/csg/csgeom.hpp
@@ -170,6 +170,8 @@ namespace netgen
     /// store splinesurfaces, such that added ones do not get deleted before geometry does
     Array<shared_ptr<SplineSurface>> spline_surfaces;
 
+    shared_ptr<BlockAllocator> solid_ball = Solid::ball;
+    
   public:
     CSGeometry ();
     CSGeometry (const string & afilename);
diff --git a/libsrc/csg/solid.cpp b/libsrc/csg/solid.cpp
index c61f4e39..d11973ab 100644
--- a/libsrc/csg/solid.cpp
+++ b/libsrc/csg/solid.cpp
@@ -1842,5 +1842,6 @@ namespace netgen
 
 
 
-  BlockAllocator Solid :: ball(sizeof (Solid));
+  // BlockAllocator Solid :: ball(sizeof (Solid));
+  shared_ptr<BlockAllocator> Solid :: ball = make_shared<BlockAllocator>(sizeof (Solid));
 }
diff --git a/libsrc/csg/solid.hpp b/libsrc/csg/solid.hpp
index 33592345..c78e6af8 100644
--- a/libsrc/csg/solid.hpp
+++ b/libsrc/csg/solid.hpp
@@ -161,15 +161,15 @@ namespace netgen
     static Solid * CreateSolid (istream & ist, const SymbolTable<Solid*> & solids);
 
 
-    static BlockAllocator ball;
+    static shared_ptr<BlockAllocator> ball;
     void * operator new(size_t /* s */) 
     {
-      return ball.Alloc();
+      return ball->Alloc();
     }
 
     void operator delete (void * p)
     {
-      ball.Free (p);
+      ball->Free (p);
     }
 
 
diff --git a/libsrc/general/optmem.cpp b/libsrc/general/optmem.cpp
index 73ca693b..40cfb4c5 100644
--- a/libsrc/general/optmem.cpp
+++ b/libsrc/general/optmem.cpp
@@ -14,7 +14,7 @@
 
 namespace netgen
 {
-  static mutex block_allocator_mutex;
+  // static mutex block_allocator_mutex;
 
   BlockAllocator :: BlockAllocator (unsigned asize, unsigned ablocks)
     : bablocks (0)
diff --git a/libsrc/general/optmem.hpp b/libsrc/general/optmem.hpp
index 658bf055..0d2b9de7 100644
--- a/libsrc/general/optmem.hpp
+++ b/libsrc/general/optmem.hpp
@@ -23,6 +23,7 @@ private:
   void * freelist;
   ///
   Array<char*> bablocks;
+  mutex block_allocator_mutex;
 public:
   ///
   BlockAllocator (unsigned asize, unsigned ablocks = 100);