diff --git a/src/Cookie.php b/src/Cookie.php
index 5ea280c..b70effa 100644
--- a/src/Cookie.php
+++ b/src/Cookie.php
@@ -163,6 +163,6 @@ class Cookie {
 
     protected function normalizeKey(string $key) : string
     {
-        return str_replace([',', ';', ' ', '='], '_', $key);
+        return str_replace([',', ';', ' ', '=', '.'], '_', $key);
     }
 }