diff --git a/lib/validate.js b/lib/validate.js
index 97cbbf6..dbc0882 100644
--- a/lib/validate.js
+++ b/lib/validate.js
@@ -202,7 +202,7 @@ var validate = exports._validate = function(/*Any*/instance,/*Object*/schema,/*O
 					if (value === undefined && options.existingOnly) continue;
 					var propDef = objTypeDef[i];
 					// set default
-					if(value === undefined && propDef["default"]){
+					if(value === undefined && propDef["default"] !== undefined){
 						value = instance[i] = propDef["default"];
 					}
 					if(options.coerce && i in instance){