diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 69482212..04f028a6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        PHP_VERSION: ["7.4", "8.0"]
+        PHP_VERSION: ["7.4", "8.0", "8.1"]
     env:
       PHP_VERSION: ${{ matrix.php_version }}
     steps:
diff --git a/src/Definition/ArrayAccessDefinitionTrait.php b/src/Definition/ArrayAccessDefinitionTrait.php
index 864e4fb7..db733336 100644
--- a/src/Definition/ArrayAccessDefinitionTrait.php
+++ b/src/Definition/ArrayAccessDefinitionTrait.php
@@ -14,6 +14,7 @@ trait ArrayAccessDefinitionTrait {
   /**
    * {@inheritdoc}
    */
+  #[\ReturnTypeWillChange]
   public function offsetExists($offset) {
     return array_key_exists($offset, $this->definition);
   }
@@ -21,6 +22,7 @@ public function offsetExists($offset) {
   /**
    * {@inheritdoc}
    */
+  #[\ReturnTypeWillChange]
   public function offsetGet($offset) {
     return $this->definition[$offset] ?? NULL;
   }
@@ -28,6 +30,7 @@ public function offsetGet($offset) {
   /**
    * {@inheritdoc}
    */
+  #[\ReturnTypeWillChange]
   public function offsetSet($offset, $value) {
     $this->definition[$offset] = $value;
   }
@@ -35,6 +38,7 @@ public function offsetSet($offset, $value) {
   /**
    * {@inheritdoc}
    */
+  #[\ReturnTypeWillChange]
   public function offsetUnset($offset) {
     unset($this->definition[$offset]);
   }