The accuracy of an annotated corpus can be increased through evaluation and revision of the annotation scheme, and through adjudication of the disagreements found. In this paper, we describe a novel process that has been applied to improve a part-of-speech (POS) tagged corpus for the African language Igbo. An inter-annotation agreement (IAA) exercise was undertaken to iteratively revise the tagset used in the creation of the initial tagged corpus, with the aim of refining the tagset and maximizing annotator performance. The tagset revisions and other corrections were efficiently propagated to the overall corpus in a semi-automated manner using transformation-based learning (TBL) to identify candidates for correction and to propose possible tag corrections. The affected word-tag pairs in the corpus were inspected to ensure a high quality end-product with an accuracy that would not be achieved through a purely automated process. The results show that the tagging accuracy increases from 88% to 94%. The tagged corpus is potentially re-usable for other dialects of the language.