diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 7e13449..9b9e24d 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4','8.0']
+        php: ['5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1']
     name: PHP ${{ matrix.php }}
     steps:
     - name: Checkout
diff --git a/src/RRule.php b/src/RRule.php
index 3c3f5c2..0c3889c 100755
--- a/src/RRule.php
+++ b/src/RRule.php
@@ -917,6 +917,7 @@ class RRule implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetExists($offset)
 	{
 		return is_numeric($offset) && $offset >= 0 && ! is_float($offset) && $offset < count($this);
@@ -925,6 +926,7 @@ class RRule implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetGet($offset)
 	{
 		if (! is_numeric($offset) || $offset < 0 || is_float($offset)) {
@@ -957,6 +959,7 @@ class RRule implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetSet($offset, $value)
 	{
 		throw new \LogicException('Setting a Date in a RRule is not supported');
@@ -965,6 +968,7 @@ class RRule implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetUnset($offset)
 	{
 		throw new \LogicException('Unsetting a Date in a RRule is not supported');
@@ -980,6 +984,7 @@ class RRule implements RRuleInterface
 	 *
 	 * @return int
 	 */
+	#[\ReturnTypeWillChange]
 	public function count()
 	{
 		if ($this->isInfinite()) {
@@ -1326,6 +1331,7 @@ class RRule implements RRuleInterface
 	 *
 	 * @return \DateTime|null
 	 */
+	#[\ReturnTypeWillChange]
 	public function getIterator()
 	{
 		$total = 0;
diff --git a/src/RSet.php b/src/RSet.php
index 7fc4a20..8a1d4e0 100755
--- a/src/RSet.php
+++ b/src/RSet.php
@@ -489,6 +489,7 @@ class RSet implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetExists($offset)
 	{
 		return is_numeric($offset) && $offset >= 0 && ! is_float($offset) && $offset < count($this);
@@ -497,6 +498,7 @@ class RSet implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetGet($offset)
 	{
 		if (! is_numeric($offset) || $offset < 0 || is_float($offset)) {
@@ -529,6 +531,7 @@ class RSet implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetSet($offset, $value)
 	{
 		throw new \LogicException('Setting a Date in a RSet is not supported (use addDate)');
@@ -537,6 +540,7 @@ class RSet implements RRuleInterface
 	/**
 	 * @internal
 	 */
+	#[\ReturnTypeWillChange]
 	public function offsetUnset($offset)
 	{
 		throw new \LogicException('Unsetting a Date in a RSet is not supported (use addDate)');
@@ -551,6 +555,7 @@ class RSet implements RRuleInterface
 	 * introduces a performance penality.
 	 * @return int
 	 */
+	#[\ReturnTypeWillChange]
 	public function count()
 	{
 		if ($this->isInfinite()) {
@@ -588,6 +593,7 @@ class RSet implements RRuleInterface
 	 * @param $reset (bool) Whether to restart the iteration, or keep going
 	 * @return \DateTime|null
 	 */
+	#[\ReturnTypeWillChange]
 	public function getIterator()
 	{
 		$previous_occurrence = null;