Extension Method for Getting All Properties of a Type

I was writing a helper class that I needed to iterate through all of the properties of a type; later realized that my code didn't grab every property, specifically those that were interface types. Then I found this at beaucrawford.net (http://beaucrawford.net/post/Using-Reflection-to-get-inherited-properties-for-an-interface.aspx). I then turned it into an extension method. Behold:

namespace System
{
    public static class TypeExtensionMethods
    {
        public static PropertyInfo[] GetAllProperties(this Type type)
        {
            List<Type> typeList = new List<Type>();
            typeList.Add(type);

            if (type.IsInterface)
            {
                typeList.AddRange(type.GetInterfaces());
            }

            List<PropertyInfo> propertyList = new List<PropertyInfo>();

            foreach (Type interfaceType in typeList)
            {
                foreach (PropertyInfo property in interfaceType.GetProperties())
                {
                    propertyList.Add(property);
                }
            }

            return propertyList.ToArray();
        }
    }
}