diff --git a/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php b/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php
index fccb3b6a3b52c897ef232900de4364d98316670e..7159bf1c2ec811b47ba024442d677aeb26b2bb83 100644
--- a/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php
+++ b/typo3/sysext/core/Classes/Authentication/AbstractUserAuthentication.php
@@ -141,7 +141,7 @@ abstract class AbstractUserAuthentication
      * Session timeout (on the server)
      *
      * If >0: session-timeout in seconds.
-     * If 0: no timeout.
+     * If <=0: Instant logout after login.
      *
      * @var int
      */
diff --git a/typo3/sysext/core/Classes/Authentication/BackendUserAuthentication.php b/typo3/sysext/core/Classes/Authentication/BackendUserAuthentication.php
index 55c8e9b24278293967a72539b6c391aa3687ee49..464bf851f8786189d50302ca48362354a8582323 100644
--- a/typo3/sysext/core/Classes/Authentication/BackendUserAuthentication.php
+++ b/typo3/sysext/core/Classes/Authentication/BackendUserAuthentication.php
@@ -252,7 +252,8 @@ class BackendUserAuthentication extends \TYPO3\CMS\Core\Authentication\AbstractU
      * Session timeout (on the server)
      *
      * If >0: session-timeout in seconds.
-     * If 0: no timeout.
+     * If <=0: Instant logout after login.
+     * The value must be at least 180 to avoid side effects.
      *
      * @var int
      */
diff --git a/typo3/sysext/frontend/Classes/Authentication/FrontendUserAuthentication.php b/typo3/sysext/frontend/Classes/Authentication/FrontendUserAuthentication.php
index 12293607249355bde9bfb0c1b9d63ec91fd41b9f..f73a78472ae1af15c0c711eacd4bc905603f03f1 100644
--- a/typo3/sysext/frontend/Classes/Authentication/FrontendUserAuthentication.php
+++ b/typo3/sysext/frontend/Classes/Authentication/FrontendUserAuthentication.php
@@ -42,7 +42,7 @@ class FrontendUserAuthentication extends AbstractUserAuthentication
      * Session timeout (on the server)
      *
      * If >0: session-timeout in seconds.
-     * If 0: no timeout.
+     * If <=0: Instant logout after login.
      *
      * @var int
      */