diff --git a/extclass.cpp b/extclass.cpp
index 5c8b44b5..e246b973 100644
--- a/extclass.cpp
+++ b/extclass.cpp
@@ -234,10 +234,10 @@ ExtensionClassBase::ExtensionClassBase(const char* name)
     try_derived_class_conversions(). If a particular conversion is impossible, all
     conversion functions will return a NULL pointer.
     
-    The function extract_from_holder() attempts to actually extract the pointer to
-    the contained object from an InstanceHolderBase (a wrapper class). A conversion
+    The function extract_object_from_holder() attempts to actually extract the pointer 
+    to the contained object from an InstanceHolderBase (a wrapper class). A conversion
     of the held object to 'T *' is allowed when the conversion 
-    'dynamic_cast<InstanceHolde<T> *>(an_instance_holder_base)' succeeds.
+    'dynamic_cast<InstanceHolder<T> *>(an_instance_holder_base)' succeeds.
 */
 void * ExtensionClassBase::try_class_conversions(InstanceHolderBase* object) const
 {
@@ -254,8 +254,7 @@ void* ExtensionClassBase::try_base_class_conversions(InstanceHolderBase* object)
     {
         if(base_classes()[i].convert == 0) 
             continue;
-        
-        void* result1 = base_classes()[i].class_object->convert_from_holder(object);
+        void* result1 = base_classes()[i].class_object->extract_object_from_holder(object);
         if (result1)
             return (*base_classes()[i].convert)(result1);
         
@@ -270,7 +269,7 @@ void* ExtensionClassBase::try_derived_class_conversions(InstanceHolderBase* obje
 {
     for (std::size_t i = 0; i < derived_classes().size(); ++i)
     {
-        void* result1 = derived_classes()[i].class_object->convert_from_holder(object);
+        void* result1 = derived_classes()[i].class_object->extract_object_from_holder(object);
         if (result1) 
             return (*derived_classes()[i].convert)(result1);
         
diff --git a/extclass.h b/extclass.h
index f1712f36..05bb8017 100644
--- a/extclass.h
+++ b/extclass.h
@@ -60,11 +60,13 @@ typedef void * (*ConversionFunction)(void *);
 
 struct BaseClassInfo
 {
-    BaseClassInfo(Class<ExtensionInstance> * t, ConversionFunction f)
+    typedef Class<ExtensionInstance> ClassObject;
+    
+    BaseClassInfo(ClassObject * t, ConversionFunction f)
     :class_object(t), convert(f)
     {}
     
-    Class<ExtensionInstance> * class_object;
+    ClassObject * class_object;
     ConversionFunction convert;
 };
 typedef BaseClassInfo DerivedClassInfo;
@@ -85,6 +87,8 @@ class ExtensionClassBase : public Class<ExtensionInstance>
     void add_setter_method(Function*, const char* name);
     void add_getter_method(Function*, const char* name);
     
+    // the purpose of try_class_conversions() and its related functions 
+    // is explained in extclass.cpp
     virtual void * try_class_conversions(InstanceHolderBase*) const;
     virtual void * try_base_class_conversions(InstanceHolderBase*) const;
     virtual void * try_derived_class_conversions(InstanceHolderBase*) const;
@@ -206,7 +210,6 @@ class PyExtensionClassConverters
             return py::PyPtr<py::ExtensionInstance>(new py::ExtensionInstance(class_));
         }
 
-
     // Convert to const T*
     friend const T* from_python(PyObject* p, py::Type<const T*>)
         { return from_python(p, py::Type<T*>()); }
@@ -442,7 +445,7 @@ class ExtensionClass
     virtual std::vector<detail::DerivedClassInfo> const & derived_classes() const;
 
     // the purpose of this function is explained in extclass.cpp
-    virtual void * convert_from_holder(InstanceHolderBase * v) const;
+    virtual void * extract_object_from_holder(InstanceHolderBase * v) const;
 
     template <class Signature>
     void add_constructor(Signature sig)
@@ -521,7 +524,7 @@ class InstancePtrHolder : public InstanceHolder<HeldType>
  public:
     HeldType* target() { return &*m_ptr; }
     PtrType& ptr() { return m_ptr; }
-
+    
     InstancePtrHolder(PtrType ptr) : m_ptr(ptr) {}
  private:
     PtrType m_ptr;
@@ -577,7 +580,7 @@ ExtensionClass<T, U>::derived_classes() const
 }
        
 template <class T, class U>
-void * ExtensionClass<T, U>::convert_from_holder(InstanceHolderBase * v) const
+void * ExtensionClass<T, U>::extract_object_from_holder(InstanceHolderBase * v) const
 {
     py::InstanceHolder<T>* held = dynamic_cast<py::InstanceHolder<T>*>(v);
     if(held) return held->target();
diff --git a/extclass_demo.cpp b/extclass_demo.cpp
index 18050f7d..0334e0cd 100644
--- a/extclass_demo.cpp
+++ b/extclass_demo.cpp
@@ -373,12 +373,14 @@ static int getX(OverloadTest * u)
 
 struct Dummy
 {
+    virtual ~Dummy() {}
     int dummy_;
 };
 
 struct Base
 {
     virtual int x() const { return 999; };
+    virtual ~Base() {}
 };
 
 // inherit Dummy so that the Base part of Concrete starts at an offset
@@ -437,6 +439,7 @@ struct CallbackTestBase
 {
   virtual int testCallback(int i) { return callback(i); }
   virtual int callback(int i) = 0;
+  virtual ~CallbackTestBase() {}
 };
 
 struct CallbackTest : public CallbackTestBase
diff --git a/subclass.h b/subclass.h
index 778f8519..732d15b2 100644
--- a/subclass.h
+++ b/subclass.h
@@ -102,7 +102,7 @@ class Class
     virtual void * try_class_conversions(InstanceHolderBase*) const { return 0; }
     virtual void * try_base_class_conversions(InstanceHolderBase*) const { return 0; }
     virtual void * try_derived_class_conversions(InstanceHolderBase*) const { return 0; }
-    virtual void * convert_from_holder(InstanceHolderBase*) const { return 0; }
+    virtual void * extract_object_from_holder(InstanceHolderBase*) const { return 0; }
 
  protected:
     void add_base(Ptr base);
diff --git a/test_extclass.py b/test_extclass.py
index 648b3e81..8861aa06 100644
--- a/test_extclass.py
+++ b/test_extclass.py
@@ -525,7 +525,7 @@ Testing base class conversions
     >>> testUpcast(der2)
     444
     >>> der2 = derived2Factory(1111)
-    >>> testDowncast2(der1)
+    >>> testDowncast2(der2)
     Traceback (innermost last):
     TypeError: extension class 'Base' is not convertible into 'Derived2'.