diff --git a/src/types.cc b/src/types.cc
index 6b340fa..066b5ac 100644
--- a/src/types.cc
+++ b/src/types.cc
@@ -19,10 +19,11 @@ namespace pEp
       )
     {}
 
+////////////////
 
     template<>
     template<>
-    message* Wrapper<::message*>::_new<PEP_msg_direction, char*>(PEP_msg_direction dir, char* s)
+    message* Wrapper<::message*>::_new<PEP_msg_direction, const char*>(PEP_msg_direction dir, const char* s)
     {
         message* m = new_message(dir);
         if(!m)
@@ -32,6 +33,14 @@ namespace pEp
         return m;
     }
 
+    template<>
+    void Wrapper<::message*>::_free(::message* m)
+    {
+        free_message(m);
+    }
+
+////////////////
+
     template<>
     template<>
     ::stringpair_t* Wrapper<::stringpair_t*>::_new(const char* key, const char* value)
@@ -51,9 +60,13 @@ namespace pEp
         return Wrapper<::stringpair_t*>::_new(key.c_str(), value.c_str());
     }
 
+    template<>
+    void Wrapper<::stringpair_t*>::_free(::stringpair_t* sp)
+    {
+        free_stringpair(sp);
+    }
 
-    Message m(PEP_dir_incoming, "Foo");
-    StringPair sp(std::string("foo"), std::string("bar"));
+////////////////
 
     template class Wrapper<::pEp_identity>;
     template class Wrapper<::stringpair_t>;
diff --git a/src/types.hh b/src/types.hh
index 809884e..18f97ec 100644
--- a/src/types.hh
+++ b/src/types.hh
@@ -19,10 +19,10 @@ namespace pEp
         EngineError(PEP_STATUS status, const char* message = nullptr);
     };
 
-    using Identity = Wrapper<::pEp_identity>;
-    using StringPair = Wrapper<::stringpair_t>;
+    using Identity = Wrapper<::pEp_identity*>;
+    using StringPair = Wrapper<::stringpair_t*>;
     
-    using Message = Wrapper<::message>;
+    using Message = Wrapper<::message*>;
 
 } // end of namespace pEp
 
diff --git a/src/wrapper.hh b/src/wrapper.hh
index 77487f2..2733539 100644
--- a/src/wrapper.hh
+++ b/src/wrapper.hh
@@ -58,14 +58,14 @@ public:
     
     Wrapper<T*>&& operator=(Wrapper<T*>&& victim)
     {
-        _free();
+        _free(value);
         value = victim.value;
         victim.value = nullptr;
     }
     
     ~Wrapper()
     {
-        _free();
+        _free(value);
     }
     
 
@@ -74,7 +74,7 @@ private:
     template<class... Args>
     T* _new(Args...);
     
-    void _free();
+    void _free(T*);
 
     T* value;
 };
diff --git a/test/unittest_stringpair.cc b/test/unittest_stringpair.cc
new file mode 100644
index 0000000..c44e821
--- /dev/null
+++ b/test/unittest_stringpair.cc
@@ -0,0 +1,10 @@
+#include <gtest/gtest.h>
+
+#include "../src/types.hh"
+
+
+TEST( StringPair, T1 )
+{
+    pEp::StringPair s1{"key", "value"};
+//    pEp::StringPair s2{ std::string{"key2"}, std::string{"value"} };
+}