diff --git a/storage/storage.go b/storage/storage.go
index e112d124ab65..e1b7400f398d 100644
--- a/storage/storage.go
+++ b/storage/storage.go
@@ -475,7 +475,7 @@ type SignedURLOptions struct {
 
 	// ContentType is the content type header the client must provide
 	// to use the generated signed URL.
-	// Optional.
+	// Required.
 	ContentType string
 
 	// Headers is a list of extension headers the client must provide