diff --git a/concat_test.go b/concat_test.go
index d551b43..9527050 100644
--- a/concat_test.go
+++ b/concat_test.go
@@ -8,7 +8,7 @@ import (
 )
 
 func BenchmarkConcat(b *testing.B) {
-	var instance image.Image
+	var instance image.Image = image.NewRGBA(image.Rect(0, 0, 0, 0))
 	pixel := SinglePixel{}
 
 	for i := 0; i < b.N; i++ {