diff --git a/lib/validate.js b/lib/validate.js
index 99c9c9c..8992d6d 100644
--- a/lib/validate.js
+++ b/lib/validate.js
@@ -207,7 +207,7 @@ var validate = exports._validate = function(/*Any*/instance,/*Object*/schema,/*O
 			}
 			
 			for(var i in objTypeDef){ 
-				if(objTypeDef.hasOwnProperty(i) && i != '__proto__'){
+				if(objTypeDef.hasOwnProperty(i) && i != '__proto__' && i != 'constructor'){
 					var value = instance[i];
 					// skip _not_ specified properties
 					if (value === undefined && options.existingOnly) continue;