An extension device for a bone anchor includes at least one tab, which includes an elongate shaft portion that forms part of a channel for providing a stabilization rod to a rod receiving recess of a receiving part of the bone anchor, and a coupling portion, which is provided at a distal end of the elongate shaft portion and which is configured to be coupled to the receiving part. The coupling portion includes a first engagement portion for engaging a first engagement face of the receiving part and a second engagement portion for engaging a second engagement face of the receiving part. A spring element is provided at the coupling portion, the spring element exerting a compression force to urge the first and second engagement portions in mutually opposite directions towards each other and towards the corresponding first and second engagement faces along a longitudinal axis defined by the extension device and the receiving part when being coupled together.
