diff --git a/src/zip.rs b/src/zip.rs
index e2772aa..d130eb4 100644
--- a/src/zip.rs
+++ b/src/zip.rs
@@ -395,7 +395,7 @@ mod tests {
             let mut zipgen = ZipGenerator::new(
                 FileSet {
                     files: vec![],
-                    directory_name: "test".to_owned(),
+                    directory_name: Some("test".to_owned()),
                 },
                 Box::new(std::io::Cursor::new(&mut output)),
             );