The problem of measuring the distance between two electronic devices in the presence of an adversary is still open. Existing approaches based on distance-bounding protocols are subject to enlargement attacks that cause the target to be perceived farther than it actually is. Enlargement attacks represent a new challenge for the research field of secure localization. The contribution of this paper is twofold. First, we propose SecDEv, a secure distance-bounding protocol for wireless channels that withstands enlargement attacks based on jam-and-replay. By leveraging on the characteristics of radio frequency signals, SecDEv establishes a security horizon within which a distance is correctly measured and a jam-and-replay attack is detected. Second, we show how SecDEv improves the scalability of secure positioning techniques.