diff --git a/lib/bunyan.js b/lib/bunyan.js
index dcd1f90..d85eb56 100644
--- a/lib/bunyan.js
+++ b/lib/bunyan.js
@@ -918,7 +918,6 @@ function safeCycles() {
 if (mv) {
 
 function RotatingFileStream(options) {
-  assert.ok(options.period, 'need a period');
   this.path = options.path;
   this.stream = fs.createWriteStream(this.path,
     {flags: 'a', encoding: 'utf8'});