A fragment of a graveslab, measuring roughly 47 centimetres by 22 centimetres, has been built into the east end of the north wall of the modern sacristy, where it serves as a quoin stone, one of the dressed corner stones used to reinforce and finish the angle of a wall. The lettering is still visible on its surface, but time and repositioning have rendered it entirely illegible.

The fragment almost certainly originated as part of a memorial graveslab, the kind of flat inscribed stone that would once have lain over a burial or been set upright to mark a grave. Such slabs were common features of medieval religious houses, often carved with the name of the deceased, a date, a family emblem, or a short prayer. At some point, this one was broken, its original context lost, and it was pressed into service as building material. The Augustinian abbey at Fethard has a long history, and the repurposing of earlier carved stonework within later building phases was a widespread and thoroughly practical habit across Irish ecclesiastical sites. The sacristy wall in which it now sits is modern, meaning the fragment passed through at least one, and quite possibly several, phases of reuse before reaching its current position.