diff --git a/src/aurelia-plugins-cookies.js b/src/aurelia-plugins-cookies.js
index af05bb2..56f9a32 100644
--- a/src/aurelia-plugins-cookies.js
+++ b/src/aurelia-plugins-cookies.js
@@ -22,7 +22,7 @@ export class Cookies {
     let str = `${this._encode(key)}=${value != null ? this._encode(value) : ''}`;
     if (options.path) str += `; path=${options.path}`;
     if (options.domain) str += `; domain=${options.domain}`;
-    if (options.expires) str += `; expires=${expires.toUTCString()}`;
+    if (expires) str += `; expires=${expires.toUTCString()}`;
     if (options.secure) str += '; secure';
     document.cookie = str;
   }
@@ -59,4 +59,4 @@ export class Cookies {
     }
     return obj;
   }
-}
\ No newline at end of file
+}