In recent years, Wi-Fi-based indoor positioning has attracted increasing research attention due to its ubiquitous deployment. Although extensive research has been conducted on Wi-Fi fingerprint-based positioning, especially, in complex environments and long-term deployments, the automatic adaptation of radio map has not been fully studied and the problems remain open. When the positions of some Access Points (APs) change, the traditional approach regularly conducts site surveying which is time-consuming and labor-intensive. In this paper, we propose a crowdsourcing indoor positioning approach based on ensemble learning for automatic Altered APs Identification and Fingerprints Updating, namely AAIFU. We propose an algorithm to detect and identify the altered APs in crowdsourcing data. After getting the altered APs, we use the relationship between the received signal strength values of the altered APs and the unaltered APs in the crowdsourcing data to train a prediction model used to update the radio map. We also handle the device diversity on all the processes of AAIFU. Our proposed solution is lightweight which does not rely on additional infrastructure and inertial sensors with high power consumption. The comprehensive experiments have been carried out in our teaching building to evaluate the effectiveness of AAIFU. The results show that our proposed AAIFU can effectively adapt the radio map to the movement of APs and improve positioning accuracy. Correspondingly, we achieve an average positioning accuracy of 2.6m which outperforms the fingerprinting approach with the original radio map by 63.9%. INDEX TERMS Indoor positioning, ensemble learning, radio map updating, crowdsourcing. The associate editor coordinating the review of this manuscript and approving it for publication was Nafees Mansoor. physical locations. Each fingerprint is a vector of Received Signal Strength (RSS) values from Wi-Fi Access Points (APs) labeled by its ground truth locations. In the online positioning stage, the mobile client collects RSS values and sends the measurement results to the server in which pattern matching algorithms are adopted to match the measured RSS with the most similar fingerprints in the database and return the associated location. To improve the accuracy of Wi-Fi fingerprint-based indoor positioning, various pattern matching algorithms have been widely investigated [2]-[5] for fingerprint matching, which are generally divided into deterministic [6]-[8] and probabilistic methods [9]-[11]. RADAR [6] as the pioneer work of indoor positioning uses the nearest neighbor algorithm as a deterministic method for fingerprint matching to find user's location from fingerprint database. HORUS [9] proposes a probabilistic method based on the signal intensity distribution