diff --git a/.env.testing b/.env.testing
index 48e0440f8..935442666 100644
--- a/.env.testing
+++ b/.env.testing
@@ -7,7 +7,7 @@ APP_LOCALE="en-US"
 APP_URL=https://pixelfed.test
 APP_DOMAIN="pixelfed.test"
 ADMIN_DOMAIN="pixelfed.test"
-SESSION_DOMAIN="pixelfed.test"
+SESSION_DOMAIN=null # Keep as null unless required for sharing session cookies with subdomains like SSO
 TRUST_PROXIES="*"
 
 LOG_CHANNEL=null