diff --git a/js/property_field.js b/js/property_field.js
index 0915504dc..86f7ee943 100644
--- a/js/property_field.js
+++ b/js/property_field.js
@@ -230,7 +230,7 @@ function ValidateWithPattern(sFieldId, bMandatory, sPattern, sFormId, aForbidden
 	}
 	if (aForbiddenValues)
 	{
-		for(var i = 0; i < aForbiddenValues.length; i++)
+		for(var i in aForbiddenValues)
 		{
 			if (aForbiddenValues[i] == currentVal)
 			{