diff --git a/XPath/impl/xpath_expression.hpp b/XPath/impl/xpath_expression.hpp
index a0bda592..0a1e2f90 100644
--- a/XPath/impl/xpath_expression.hpp
+++ b/XPath/impl/xpath_expression.hpp
@@ -39,7 +39,11 @@ private:
   XPathExpression& operator=(const XPathExpression&);
 }; // class XPathExpression
 
-typedef boost::shared_ptr<XPathExpression> XPathExpressionPtr;
+class XPathExpressionPtr : public boost::shared_ptr<XPathExpression> 
+{ 
+public:
+  explicit XPathExpressionPtr(XPathExpression* xp) : boost::shared_ptr<XPathExpression>(xp) { }
+};
 
 class UnaryExpression
 {
diff --git a/XPath/impl/xpath_function_resolver.hpp b/XPath/impl/xpath_function_resolver.hpp
index 8bb01fdb..3b5717b5 100644
--- a/XPath/impl/xpath_function_resolver.hpp
+++ b/XPath/impl/xpath_function_resolver.hpp
@@ -1,16 +1,13 @@
 #ifndef ARABICA_XPATH_FUNCTION_RESOLVER_HPP
 #define ARABICA_XPATH_FUNCTION_RESOLVER_HPP
 
-#include <boost/shared_ptr.hpp>
-
 namespace Arabica
 {
 namespace XPath
 {
 
 class XPathFunction;
-class XPathExpression;
-typedef boost::shared_ptr<XPathExpression> XPathExpressionPtr;
+class XPathExpressionPtr;
 
 class UndefinedFunctionException : public std::runtime_error
 {
diff --git a/XPath/impl/xpath_object.hpp b/XPath/impl/xpath_object.hpp
index dbe48014..b8a76687 100644
--- a/XPath/impl/xpath_object.hpp
+++ b/XPath/impl/xpath_object.hpp
@@ -13,11 +13,6 @@ namespace Arabica
 namespace XPath
 {
 
-class XPathExpression;
-typedef boost::shared_ptr<XPathExpression> XPathExpressionPtr;
-class XPathValue;
-typedef boost::shared_ptr<const XPathValue> XPathValuePtr;
-
 enum ValueType
 {
   ANY ,
@@ -122,6 +117,12 @@ private:
   XPathValue& operator=(const XPathValue&);
 }; // class XPathValue
 
+class XPathValuePtr : public boost::shared_ptr<const XPathValue> 
+{ 
+public:
+  explicit XPathValuePtr(const XPathValue* v) : boost::shared_ptr<const XPathValue>(v) { }
+};
+
 const double NaN = std::sqrt(-2.0);
 const double Zero = 0.0;
 const double Negative_Zero = -Zero;
diff --git a/XPath/impl/xpath_variable_resolver.hpp b/XPath/impl/xpath_variable_resolver.hpp
index 6fe95af2..fc17d5b2 100644
--- a/XPath/impl/xpath_variable_resolver.hpp
+++ b/XPath/impl/xpath_variable_resolver.hpp
@@ -1,17 +1,14 @@
 #ifndef ARABICA_XPATH_VARIABLE_RESOLVER_HPP
 #define ARABICA_XPATH_VARIABLE_RESOLVER_HPP
 
-#include <boost/shared_ptr.hpp>
 #include <stdexcept>
+#include "xpath_object.hpp"
 
 namespace Arabica
 {
 namespace XPath
 {
 
-class XPathValue;
-typedef boost::shared_ptr<const XPathValue> XPathValuePtr;
-
 class UnboundVariableException : public std::runtime_error
 {
 public: