diff --git a/test/pointer_traits_test.cpp b/test/pointer_traits_test.cpp
index 1455e87..368b19b 100644
--- a/test/pointer_traits_test.cpp
+++ b/test/pointer_traits_test.cpp
@@ -38,6 +38,8 @@ class CompleteSmartPtr
 {
    template <class U>
    friend class CompleteSmartPtr;
+   void unspecified_bool_type_func() const {}
+   typedef void (CompleteSmartPtr::*unspecified_bool_type)() const;
 
    public:
    #if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
@@ -73,17 +75,32 @@ class CompleteSmartPtr
    T & operator *() const
    {  return *ptr_;  }
 
+   operator unspecified_bool_type() const
+   {  return m_ptr? &CompleteSmartPtr::unspecified_bool_type_func : 0;   }
+
    template<class U>
    static CompleteSmartPtr static_cast_from(const CompleteSmartPtr<U> &uptr)
-   {  ++CompleteSmartPtrStats::static_cast_called; return CompleteSmartPtr(*static_cast<element_type*>(uptr.ptr_));  }
+   {
+      ++CompleteSmartPtrStats::static_cast_called;
+      element_type* const p = static_cast<element_type*>(uptr.ptr_);
+      return p ? CompleteSmartPtr(*p) : CompleteSmartPtr();
+   }
 
    template<class U>
    static CompleteSmartPtr const_cast_from(const CompleteSmartPtr<U> &uptr)
-   {  ++CompleteSmartPtrStats::const_cast_called; return CompleteSmartPtr(*const_cast<element_type*>(uptr.ptr_));  }
-
+   {
+      ++CompleteSmartPtrStats::const_cast_called; 
+      element_type* const p = const_cast<element_type*>(uptr.ptr_);
+      return p ? CompleteSmartPtr(*p) : CompleteSmartPtr();
+   }
+  
    template<class U>
    static CompleteSmartPtr dynamic_cast_from(const CompleteSmartPtr<U> &uptr)
-   {  ++CompleteSmartPtrStats::dynamic_cast_called; return CompleteSmartPtr(*dynamic_cast<element_type*>(uptr.ptr_));  }
+   {
+      ++CompleteSmartPtrStats::dynamic_cast_called; 
+      element_type* const p = dynamic_cast<element_type*>(uptr.ptr_);
+      return p ? CompleteSmartPtr(*p) : CompleteSmartPtr();
+   }
 
    friend bool operator ==(const CompleteSmartPtr &l, const CompleteSmartPtr &r)
    {  return l.ptr_ == r.ptr_; }
@@ -99,6 +116,8 @@ class CompleteSmartPtr
 template<class T>
 class SimpleSmartPtr
 {
+   void unspecified_bool_type_func() const {}
+   typedef void (SimpleSmartPtr::*unspecified_bool_type)() const;
    public:
 
    SimpleSmartPtr()
@@ -127,6 +146,9 @@ class SimpleSmartPtr
    T & operator *() const
    {  return *ptr_;  }
 
+   operator unspecified_bool_type() const
+   {  return ptr_? &SimpleSmartPtr::unspecified_bool_type_func : 0;   }
+
    private:
    T *ptr_;
 };