diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 7780879b..d871af55 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -13,7 +13,7 @@ on:
       - v*.*
 
 env:
-  php-extensions: mbstring, intl, mysqli, pgsql, sqlsrv-5.9.0beta2
+  php-extensions: mbstring, intl, mysqli, pgsql, sqlsrv-5.10.0-beta1
   php-extensions-key: v2
   php-tools: "composer:v2, pecl"
 
@@ -25,7 +25,7 @@ jobs:
 
     strategy:
       matrix:
-        php-version: [ '7.4', '8.0' ]
+        php-version: [ '7.4', '8.0', '8.1' ]
 
     steps:
       - name: Checkout
@@ -59,7 +59,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php-version: [ '7.1', '7.2', '7.3', '7.4', '8.0' ]
+        php-version: [ '7.1', '7.2', '7.3', '7.4', '8.0', '8.1' ]
         deps: [ 'lowest', 'newest' ]
         exclude:
           - php-version: '7.2'
@@ -70,6 +70,8 @@ jobs:
             deps: lowest
           - php-version: '8.0'
             deps: lowest
+          - php-version: '8.1'
+            deps: lowest
 
     runs-on: ubuntu-latest
 
diff --git a/src/Collection/EntityIterator.php b/src/Collection/EntityIterator.php
index 06a5e40a..4e60291c 100644
--- a/src/Collection/EntityIterator.php
+++ b/src/Collection/EntityIterator.php
@@ -63,6 +63,7 @@ public function current(): IEntity
 	}
 
 
+	#[\ReturnTypeWillChange]
 	public function key()
 	{
 		return $this->position;
diff --git a/src/Collection/ICollection.php b/src/Collection/ICollection.php
index adff093c..abf66278 100644
--- a/src/Collection/ICollection.php
+++ b/src/Collection/ICollection.php
@@ -190,7 +190,7 @@ public function fetchPairs(?string $key = null, ?string $value = null): array;
 	 * @return Iterator<int, IEntity>
 	 * @phpstan-return Iterator<int, E>
 	 */
-	public function getIterator();
+	public function getIterator(): Iterator;
 
 
 	/**
diff --git a/src/Collection/MultiEntityIterator.php b/src/Collection/MultiEntityIterator.php
index 794e76fa..d3311e93 100644
--- a/src/Collection/MultiEntityIterator.php
+++ b/src/Collection/MultiEntityIterator.php
@@ -81,6 +81,7 @@ public function current(): IEntity
 	}
 
 
+	#[\ReturnTypeWillChange]
 	public function key()
 	{
 		return $this->position;
diff --git a/src/Entity/Reflection/PropertyMetadata.php b/src/Entity/Reflection/PropertyMetadata.php
index 0e982d33..3310c79a 100644
--- a/src/Entity/Reflection/PropertyMetadata.php
+++ b/src/Entity/Reflection/PropertyMetadata.php
@@ -189,7 +189,7 @@ public function isValid(&$value): bool
 					$value = $tmp->setTimezone(new DateTimeZone(date_default_timezone_get()));
 					return true;
 
-				} elseif (ctype_digit($value)) {
+				} elseif (ctype_digit((string) $value)) {
 					$value = new $rawType("@{$value}");
 					return true;
 				}