In this paper we propose an algorithm for computing the full lemma of German verbs that occur in sentences with a separated prefix. The algorithm is meant for large-scale corpus annotation. It relies on Part-of-Speech tags and works with 97% precision when the tags are correct. Unfortunately there are multi-word adverbs with particles that are homographs with separated verb particles and prepositions. Since the usage as separated particle and preposition is much more frequent, these multi-word adverbs are often incorrectly tagged. We show that special treatment of these bi-particle adverbs improves the re-attachment of separated verb particles.