This article investigates variant forms of the demonstrative ‘that’ and the adjective in the Caligula Manuscript of Laȝamon's Brut and concludes that they to a large extent maintain the traditional category distinction between the accusative and the dative by the use of the suffixes -ne and -Vn (where V stands for any vowel) respectively. There are, however, factors that potentially compromise the status of these terminations as case markers: phonetic reduction (which has often been invoked), capricious addition or deletion of final e, occasional doubling or simplification of nasals, and simply unexpected choices of forms in the paradigm. These seem to be consistent with the sort of mistakes that scribes might occasionally make when faced with an original that has a different orthographical and morphological system from their own, and they are not as disruptive of the case-marking system as at first sight they might appear. For one thing, they occur rather rarely and are generally outnumbered by historically expected forms; for another, the resultant unexpected case forms, usually with the stem vowel preferred by the historical forms in the case of the demonstrative, are predominantly accompanied by a historically motivated case form of their head noun. The status of accusative -ne and dative -Vn, in fact, appears to be stable enough to lead to the development of a system or subsystem of indicating case regardless of gender considerations in their respective case contexts. These suffixes can therefore be treated validly as independent case markers, although in concrete cases the possibility always exists that there is an optional final e, an unhistorical double or single n, or an unexpected choice of inflectional forms.