Seven elements are enough for max value of int64.
diff --git a/comma.go b/comma.go
index 9d0d2ed..20711c1 100644
--- a/comma.go
+++ b/comma.go
@@ -18,7 +18,7 @@
 		v = 0 - v
 	}
 
-	parts := []string{"", "", "", "", "", "", "", ""}
+	parts := []string{"", "", "", "", "", "", ""}
 	j := len(parts) - 1
 
 	for v > 999 {