diff --git a/src/Saml2/Auth.php b/src/Saml2/Auth.php
index 63fb5b54..f4dfdbb5 100644
--- a/src/Saml2/Auth.php
+++ b/src/Saml2/Auth.php
@@ -220,6 +220,7 @@ public function setSchemasPath($path)
      * Process the SAML Response sent by the IdP.
      *
      * @param string|null $requestId The ID of the AuthNRequest sent by this SP to the IdP
+     * @phpstan-return ($stay is true ? string : never)
      *
      * @throws Error
      * @throws ValidationError
@@ -270,6 +271,7 @@ public function processResponse($requestId = null)
      * @param bool        $stay                         True if we want to stay (returns the url string) False to redirect
      *
      * @return string|null
+     * @phpstan-return ($stay is true ? string : never)
      *
      * @throws Error
      */
@@ -352,6 +354,7 @@ public function processSLO($keepLocalSession = false, $requestId = null, $retrie
      * @param bool   $stay       True if we want to stay (returns the url string) False to redirect
      *
      * @return string|null
+     * @phpstan-return ($stay is true ? string : never)
      */
     public function redirectTo($url = '', array $parameters = array(), $stay = false)
     {
@@ -533,6 +536,7 @@ public function getAttributeWithFriendlyName($friendlyName)
      * @param string      $nameIdValueReq  Indicates to the IdP the subject that should be authenticated
      *
      * @return string|null If $stay is True, it return a string with the SLO URL + LogoutRequest + parameters
+     * @phpstan-return ($stay is true ? string : never)
      *
      * @throws Error
      */
@@ -573,6 +577,7 @@ public function login($returnTo = null, array $parameters = array(), $forceAuthn
      * @param string|null $nameIdNameQualifier The NameID NameQualifier will be set in the LogoutRequest.
      *
      * @return string|null If $stay is True, it return a string with the SLO URL + LogoutRequest + parameters
+     * @phpstan-return ($stay is true ? string : never)
      *
      * @throws Error
      */
diff --git a/src/Saml2/Utils.php b/src/Saml2/Utils.php
index 517ff50f..cb9def98 100644
--- a/src/Saml2/Utils.php
+++ b/src/Saml2/Utils.php
@@ -310,6 +310,7 @@ public static function getStringBetween($str, $start, $end)
      * @param bool   $stay       True if we want to stay (returns the url string) False to redirect
      *
      * @return string|null $url
+     * @phpstan-return ($stay is true ? string : never)
      *
      * @throws Error
      */
@@ -916,6 +917,7 @@ public static function parseDuration($duration, $timestamp = null)
      * @param string|int|null $validUntil    The valid until date, as a string or as a timestamp
      *
      * @return int|null $expireTime  The expiration time.
+     * @phpstan-return ($cacheDuration is true ? string : never)
      *
      * @throws Exception
      */