diff --git a/src/code/graph.c b/src/code/graph.c
index 8a4646808f..63c2fdba91 100644
--- a/src/code/graph.c
+++ b/src/code/graph.c
@@ -141,6 +141,9 @@ void Graph_InitTHGA(GraphicsContext* gfxCtx) {
     gfxCtx->overlayBuffer = pool->overlayBuffer;
     gfxCtx->workBuffer = pool->workBuffer;
 
+    //! @bug fbIdx is a signed integer that can overflow into the negatives. When compiled with IDO, the remainder
+    //! operator will yield -1 for odd negative values of fbIdx (i.e. the same as C99 onwards).
+    //! This results in an out of bounds array access in SysCfb_GetFbPtr due to the negative index value.
     gfxCtx->curFrameBuffer = SysCfb_GetFbPtr(gfxCtx->fbIdx % 2);
     gfxCtx->unk_014 = 0;
 }