Peer-to-peer systems provide scalable distribution of content for cheap and resist to censorship attempts. However, P2P networks mainly distribute immutable contents and provide poor support for highly dynamic contents produced by collaborative systems. A new class of algorithms called CRDT (Commutative Replicated Data Type) are emerging for ensuring consistency of highly dynamic content on P2P networks. However, if existing CRDT algorithms support the "edit anywhere, anytime" feature, they do not support the "undo anywhere, anytime" feature. In this paper, we present the Logoot-Undo CRDT algorithm that integrates the "undo anywhere, anytime" feature. We compare the performance of the proposed algorithm with related algorithms and measure the impact of the undo feature on the global performance of the algorithm. We prove that the cost of the undo feature remains low on a corpus of data extracted from Wikipedia.