diff --git a/winarea_d2d/ui.h b/winarea_d2d/ui.h
index 1a7f883c..ab888256 100644
--- a/winarea_d2d/ui.h
+++ b/winarea_d2d/ui.h
@@ -79,6 +79,7 @@ uiDrawPath *uiDrawNewPath(uiDrawFillMode);
 void uiDrawPathNewFigure(uiDrawPath *, double, double);
 void uiDrawPathLineTo(uiDrawPath *, double, double);
 // notes: angles are both relative to 0 and go counterclockwise
+// TODO is the initial line segment on cairo and OS X a proper join?
 void uiDrawPathArcTo(uiDrawPath *, double, double, double, double, double);
 void uiDrawPathBezierTo(uiDrawPath *, double, double, double, double, double, double);
 void uiDrawPathCloseFigure(uiDrawPath *);