diff --git a/src/DataStructures/StrictQueue.php b/src/DataStructures/StrictQueue.php
index 2401859..daa065c 100644
--- a/src/DataStructures/StrictQueue.php
+++ b/src/DataStructures/StrictQueue.php
@@ -47,7 +47,7 @@ class StrictQueue extends StrictList
      *
      * @throws \RuntimeException
      */
-    public function setIteratorMode(int $mode): int
+    final public function setIteratorMode(int $mode): int
     {
         if ($mode > 1) {
             throw new RuntimeException('Changing the iterator direction of ' . static::class . ' is prohibited.');
diff --git a/src/DataStructures/StrictStack.php b/src/DataStructures/StrictStack.php
index ee90be1..71f73c6 100644
--- a/src/DataStructures/StrictStack.php
+++ b/src/DataStructures/StrictStack.php
@@ -47,7 +47,7 @@ class StrictStack extends StrictList
      *
      * @throws \RuntimeException
      */
-    public function setIteratorMode(int $mode): int
+    final public function setIteratorMode(int $mode): int
     {
         if ($mode < 2) {
             throw new RuntimeException('Changing the iterator direction of ' . static::class . ' is prohibited.');