Internet of things is one of the most important and rapidly evolving trends of our time in computer science and informatics. Software, which enables data processing and device connectivity in the internet of things is called IoT platform. There are plenty of them in the market, but only few of them are open source and based on open standards as oneM2M. One of those platforms is called OM2M, but unfortunately it does not support complex event processing, which is very important for a number of scenarios in IoT. For this purpose, we decided that we will upgrade OM2M platform with that functionality in such a way that the entire architecture will still be consistent with open standards. Implemented extension does not change the OM2M platform in any way and it uses exclusively open source libraries. It allows developers to use it in different ways and is designed to support many scenarios used in the world of internet of things. The upgrade is available as a plug-in or library, which can be simply included in the project of OM2M platform.