diff --git a/src/common/singletonfactory.hpp b/src/common/singletonfactory.hpp
index 0065227df..0f6a12755 100644
--- a/src/common/singletonfactory.hpp
+++ b/src/common/singletonfactory.hpp
@@ -35,7 +35,7 @@ This code is heavily inspired by
 #define LUMIERA_SINGLETONFACTORY_H
 
 
-#include "common/singletonpolicies.hpp"  ///< several Policies usable together with SingletonFactory
+#include "common/singletonpolicies.hpp"  // several Policies usable together with SingletonFactory
 
 #include "common/util.hpp"
 #include "proc/nobugcfg.hpp"
diff --git a/src/proc/mobject/session/defsmanager.cpp b/src/proc/mobject/session/defsmanager.cpp
index b60e38064..383b1f60f 100644
--- a/src/proc/mobject/session/defsmanager.cpp
+++ b/src/proc/mobject/session/defsmanager.cpp
@@ -51,6 +51,13 @@ namespace mobject
     }
     
     
+    
+    /** @internal causes boost::checked_delete from \c scoped_ptr<DefsRegistry>
+     *  to be placed here, where the declaration of DefsRegistry is available.*/
+    DefsManager::~DefsManager() {}
+    
+    
+    
     template<class TAR>
     P<TAR>
     DefsManager::search  (const Query<TAR>& capabilities)
diff --git a/src/proc/mobject/session/defsmanager.hpp b/src/proc/mobject/session/defsmanager.hpp
index eb2ca1502..12bc039f8 100644
--- a/src/proc/mobject/session/defsmanager.hpp
+++ b/src/proc/mobject/session/defsmanager.hpp
@@ -33,14 +33,15 @@
 
 
 
-namespace mobject
-  {
-  namespace session
-    {
+namespace mobject {
+  namespace session {
+    
+    
     using lumiera::P;
     using boost::scoped_ptr;
     
     class DefsRegistry;
+    class SessManagerImpl;
 
 
     /**
@@ -63,6 +64,8 @@ namespace mobject
         friend class SessManagerImpl;
         
       public:
+       ~DefsManager ();
+       
         /** common access point: retrieve the default object fulfilling
          *  some given conditions. May silently trigger object creation.
          *  @throw error::Config in case no solution is possible, which
diff --git a/src/proc/mobject/session/session.cpp b/src/proc/mobject/session/session.cpp
index 5c4bb8592..d8d20ed4c 100644
--- a/src/proc/mobject/session/session.cpp
+++ b/src/proc/mobject/session/session.cpp
@@ -32,9 +32,8 @@
 
 
 #include "proc/mobject/session.hpp"
-#include "proc/mobject/session/sessionimpl.hpp"
 #include "proc/mobject/session/defsmanager.hpp"
-#include "proc/mobject/session/defsregistry.hpp"
+#include "proc/mobject/session/sessionimpl.hpp"
 
 #include "common/singleton.hpp"
 
diff --git a/src/proc/mobject/session/sessionimpl.hpp b/src/proc/mobject/session/sessionimpl.hpp
index 89e3c020a..a56fdb217 100644
--- a/src/proc/mobject/session/sessionimpl.hpp
+++ b/src/proc/mobject/session/sessionimpl.hpp
@@ -94,6 +94,8 @@ namespace mobject
         friend class lumiera::singleton::StaticCreate<SessManagerImpl>;
         
       public:
+        virtual ~SessManagerImpl() {}
+        
         virtual void clear () ;
         virtual void reset () ;
         virtual void load ()  ;
diff --git a/src/proc/mobject/session/sessmanagerimpl.cpp b/src/proc/mobject/session/sessmanagerimpl.cpp
index 8195e4fbe..7ac96bee4 100644
--- a/src/proc/mobject/session/sessmanagerimpl.cpp
+++ b/src/proc/mobject/session/sessmanagerimpl.cpp
@@ -39,7 +39,7 @@
 #include "proc/mobject/session.hpp"
 #include "proc/mobject/session/sessionimpl.hpp"
 #include "proc/mobject/session/defsmanager.hpp"
-#include "proc/mobject/session/defsregistry.hpp"
+//#include "proc/mobject/session/defsregistry.hpp"
 #include "common/error.hpp"
 
 using boost::scoped_ptr;