With the rise the of the Internet of Things (IoT) the Routing Protocol for Low Power and Lossy Networks (RPL) gained a lot of interest in the research community mainly for its flexibility to cope with different network topologies and its ability to offer features like Auto-Configuration, Self-Healing, Loop avoidance and detection, etc. Based on certain routing metrics, RPL's Objective Function (OF) assigns ranks to the nodes in the network then selects and optimizes the routes. This paper overviews the most used objective functions then proposes a modification on the Minimum Rank with Hysteresis Objective Function (MRHOF) which takes into consideration two metrics instead of one, to get more reliable and optimized routes.