diff --git a/lib/core/io.js b/lib/core/io.js
index f630cda3..33b20c24 100644
--- a/lib/core/io.js
+++ b/lib/core/io.js
@@ -689,8 +689,7 @@ function initWriter(writer) {
 	if (writable.size === UNDEFINED_VALUE) {
 		writable.size = 0;
 	}
-	const splitZipFile = writer instanceof SplitDataWriter;
-	if (!splitZipFile) {
+	if (!(writer instanceof SplitDataWriter)) {
 		Object.assign(writer, {
 			diskNumber: 0,
 			diskOffset: 0,