diff --git a/plug-ins/gfig/gfig-arc.c b/plug-ins/gfig/gfig-arc.c
index a2f6fcc70d..fdace8957e 100644
--- a/plug-ins/gfig/gfig-arc.c
+++ b/plug-ins/gfig/gfig-arc.c
@@ -270,7 +270,7 @@ arc_details (GdkPoint *vert_a,
   if (ay == by || by == cy || ay == cy)
     {
       /* Horz line -> midpoint gives inter_y */
-      if (ax == bx && bx == cx)
+      if (ay == by && by == cy)
         {
           /* Straight line */
           double minx = ax;