diff --git a/src/ExpressionParser.php b/src/ExpressionParser.php
index 6ac11cb56..f00e780a5 100644
--- a/src/ExpressionParser.php
+++ b/src/ExpressionParser.php
@@ -96,10 +96,7 @@ class ExpressionParser
         return $expr;
     }
 
-    /**
-     * @return ArrowFunctionExpression|null
-     */
-    private function parseArrow()
+    private function parseArrow(): ?ArrowFunctionExpression
     {
         $stream = $this->parser->getStream();
 
diff --git a/src/ExtensionSet.php b/src/ExtensionSet.php
index 20c6ba448..b0c9e9f1b 100644
--- a/src/ExtensionSet.php
+++ b/src/ExtensionSet.php
@@ -34,7 +34,7 @@ final class ExtensionSet
     private array $extensions;
     private bool $initialized = false;
     private bool $runtimeInitialized = false;
-    private $staging;
+    private StagingExtension $staging;
 
     /**
      * @var TokenParserInterface[]
diff --git a/src/Lexer.php b/src/Lexer.php
index b4fde986c..0c00c4604 100644
--- a/src/Lexer.php
+++ b/src/Lexer.php
@@ -88,7 +88,7 @@ class Lexer
         ], $options);
     }
 
-    private function initialize()
+    private function initialize(): void
     {
         if ($this->isInitialized) {
             return;
@@ -525,7 +525,7 @@ class Lexer
         }
     }
 
-    private function pushToken($type, $value = ''): void
+    private function pushToken(int $type, $value = ''): void
     {
         // do not push empty text tokens
         if (Token::TEXT_TYPE === $type && '' === $value) {
@@ -535,7 +535,7 @@ class Lexer
         $this->tokens[] = new Token($type, $value, $this->lineno);
     }
 
-    private function moveCursor($text): void
+    private function moveCursor(string $text): void
     {
         $this->cursor += \strlen($text);
         $this->lineno += substr_count($text, "\n");
diff --git a/src/Loader/ChainLoader.php b/src/Loader/ChainLoader.php
index 4c04dd8d4..1f0a6a393 100644
--- a/src/Loader/ChainLoader.php
+++ b/src/Loader/ChainLoader.php
@@ -29,7 +29,7 @@ final class ChainLoader implements LoaderInterface
     /**
      * @var array<string, bool>
      */
-    private $hasSourceCache = [];
+    private array $hasSourceCache = [];
 
     /**
      * @param iterable<LoaderInterface> $loaders
diff --git a/src/Node/Expression/Test/DefinedTest.php b/src/Node/Expression/Test/DefinedTest.php
index 10a26e0a7..d3ad881a0 100644
--- a/src/Node/Expression/Test/DefinedTest.php
+++ b/src/Node/Expression/Test/DefinedTest.php
@@ -60,7 +60,7 @@ class DefinedTest extends TestExpression
         parent::__construct($node, $name, $arguments, $lineno);
     }
 
-    private function changeIgnoreStrictCheck(GetAttrExpression $node)
+    private function changeIgnoreStrictCheck(GetAttrExpression $node): void
     {
         $node->setAttribute('optimizable', false);
         $node->setAttribute('ignore_strict_check', true);
diff --git a/src/Node/NameDeprecation.php b/src/Node/NameDeprecation.php
index 63ab28576..131c29369 100644
--- a/src/Node/NameDeprecation.php
+++ b/src/Node/NameDeprecation.php
@@ -18,9 +18,9 @@ namespace Twig\Node;
  */
 class NameDeprecation
 {
-    private $package;
-    private $version;
-    private $newName;
+    private string $package;
+    private string $version;
+    private string $newName;
 
     public function __construct(string $package = '', string $version = '', string $newName = '')
     {
diff --git a/src/Node/Node.php b/src/Node/Node.php
index bcddd4a7d..0fea4ca54 100644
--- a/src/Node/Node.php
+++ b/src/Node/Node.php
@@ -32,9 +32,9 @@ class Node implements \Countable, \IteratorAggregate
     private ?Source $sourceContext = null;
 
     /** @var array<string, NameDeprecation> */
-    private $nodeNameDeprecations = [];
+    private array $nodeNameDeprecations = [];
     /** @var array<string, NameDeprecation> */
-    private $attributeNameDeprecations = [];
+    private array $attributeNameDeprecations = [];
 
     /**
      * @param array  $nodes      An array of named nodes
diff --git a/src/NodeVisitor/EscaperNodeVisitor.php b/src/NodeVisitor/EscaperNodeVisitor.php
index 93cff933d..8b28f798d 100644
--- a/src/NodeVisitor/EscaperNodeVisitor.php
+++ b/src/NodeVisitor/EscaperNodeVisitor.php
@@ -182,7 +182,7 @@ final class EscaperNodeVisitor implements NodeVisitorInterface
         return \in_array($type, $safe) || \in_array('all', $safe);
     }
 
-    private function needEscaping()
+    private function needEscaping(): string|false
     {
         if (\count($this->statusStack)) {
             return $this->statusStack[\count($this->statusStack) - 1];
diff --git a/src/NodeVisitor/SafeAnalysisNodeVisitor.php b/src/NodeVisitor/SafeAnalysisNodeVisitor.php
index 902f765a1..8964ddb7e 100644
--- a/src/NodeVisitor/SafeAnalysisNodeVisitor.php
+++ b/src/NodeVisitor/SafeAnalysisNodeVisitor.php
@@ -28,8 +28,8 @@ use Twig\Node\Node;
  */
 final class SafeAnalysisNodeVisitor implements NodeVisitorInterface
 {
-    private $data = [];
-    private $safeVars = [];
+    private array $data = [];
+    private array $safeVars = [];
 
     public function setSafeVars(array $safeVars): void
     {
diff --git a/src/Profiler/Dumper/BlackfireDumper.php b/src/Profiler/Dumper/BlackfireDumper.php
index bb3fbb52a..7cfae16f1 100644
--- a/src/Profiler/Dumper/BlackfireDumper.php
+++ b/src/Profiler/Dumper/BlackfireDumper.php
@@ -40,7 +40,7 @@ EOF;
         return $str;
     }
 
-    private function dumpChildren(string $parent, Profile $profile, &$data)
+    private function dumpChildren(string $parent, Profile $profile, &$data): void
     {
         foreach ($profile as $p) {
             if ($p->isTemplate()) {
@@ -53,7 +53,7 @@ EOF;
         }
     }
 
-    private function dumpProfile(string $edge, Profile $profile, &$data)
+    private function dumpProfile(string $edge, Profile $profile, &$data): void
     {
         if (isset($data[$edge])) {
             ++$data[$edge]['ct'];
diff --git a/src/Runtime/EscaperRuntime.php b/src/Runtime/EscaperRuntime.php
index 64b82e6c7..664ef6092 100644
--- a/src/Runtime/EscaperRuntime.php
+++ b/src/Runtime/EscaperRuntime.php
@@ -18,7 +18,7 @@ use Twig\Markup;
 final class EscaperRuntime implements RuntimeExtensionInterface
 {
     /** @var array<string, callable(string $string, string $charset): string> */
-    private $escapers = [];
+    private array $escapers = [];
 
     /** @internal */
     public array $safeClasses = [];
@@ -316,7 +316,7 @@ final class EscaperRuntime implements RuntimeExtensionInterface
         }
     }
 
-    private function convertEncoding(string $string, string $to, string $from)
+    private function convertEncoding(string $string, string $to, string $from): string
     {
         if (!\function_exists('iconv')) {
             throw new RuntimeError('Unable to convert encoding: required function iconv() does not exist. You should install ext-iconv or symfony/polyfill-iconv.');
diff --git a/src/Test/NodeTestCase.php b/src/Test/NodeTestCase.php
index 799f0877a..14d4d47e3 100644
--- a/src/Test/NodeTestCase.php
+++ b/src/Test/NodeTestCase.php
@@ -19,10 +19,7 @@ use Twig\Node\Node;
 
 abstract class NodeTestCase extends TestCase
 {
-    /**
-     * @var Environment
-     */
-    private $currentEnv;
+    private Environment $currentEnv;
 
     abstract public function getTests();
 
diff --git a/src/Token.php b/src/Token.php
index 2f5228c37..fe1738a99 100644
--- a/src/Token.php
+++ b/src/Token.php
@@ -18,8 +18,8 @@ namespace Twig;
 final class Token
 {
     private $value;
-    private $type;
-    private $lineno;
+    private int $type;
+    private int $lineno;
 
     public const EOF_TYPE = -1;
     public const TEXT_TYPE = 0;