diff --git a/a8/xvalue.cc b/a8/xvalue.cc
index 4d68eda..b25cb03 100644
--- a/a8/xvalue.cc
+++ b/a8/xvalue.cc
@@ -69,6 +69,12 @@ namespace a8
         Set(v);
     }
 
+    XValue::XValue(void* userdata)
+    {
+        type_ = XVT_NULL;
+        Set(userdata);
+    }
+
     XValue::XValue(const char* v)
     {
         type_ = XVT_NULL;
diff --git a/a8/xvalue.h b/a8/xvalue.h
index cbc1fda..c4e1306 100644
--- a/a8/xvalue.h
+++ b/a8/xvalue.h
@@ -25,6 +25,7 @@ namespace a8
         XValue(long v);
         XValue(unsigned long v);
         XValue(double v);
+        XValue(void* userdata);
         XValue(const char* v);
         XValue(const std::string& v);
         XValue(std::string& v);