diff --git a/extension/background.js b/extension/background.js
index 6883f66..f10a1a8 100644
--- a/extension/background.js
+++ b/extension/background.js
@@ -164,7 +164,7 @@ function buildCookieLine(cookie) {
         "TRUE",
         cookie.path,
         cookie.httpOnly.toString().toUpperCase(),
-        cookie.expirationDate,
+        Math.trunc(cookie.expirationDate) || 0,
         cookie.name,
         cookie.value,
     ].join("\t");