diff --git a/x/canvas/draw.go b/x/canvas/draw.go
index 187528e..678d480 100644
--- a/x/canvas/draw.go
+++ b/x/canvas/draw.go
@@ -215,7 +215,7 @@ type fillingContext struct {
 }
 
 func (context *fillingContext) fillPolygonHotOpaque () {
-	for index := 0; index < len(context.boundaries); index += 2 {
+	for index := 0; index < len(context.boundaries) - 1; index += 2 {
 		left  := context.boundaries[index]
 		right := context.boundaries[index + 1]
 
@@ -240,7 +240,7 @@ func (context *fillingContext) fillPolygonHotOpaque () {
 }
 
 func (context *fillingContext) fillPolygonHotTransparent () {
-	for index := 0; index < len(context.boundaries); index += 2 {
+	for index := 0; index < len(context.boundaries) - 1; index += 2 {
 		left  := context.boundaries[index]
 		right := context.boundaries[index + 1]