diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index b7333e2..96b6c71 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -31,7 +31,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        php: ['7.4', '8.0', '8.1', '8.2', '8.3']
+        php: ['7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
     steps:
       - name: Checkout
         uses: actions/checkout@v2
diff --git a/phpstan.neon b/phpstan.neon
index 48e664e..e602b7c 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,6 @@
 parameters:
 	level: 5
+	treatPhpDocTypesAsCertain: false
 	paths:
 		- src
 		#- tests
diff --git a/src/GraphicsState.php b/src/GraphicsState.php
index 27feafb..f8da2b1 100644
--- a/src/GraphicsState.php
+++ b/src/GraphicsState.php
@@ -26,10 +26,12 @@ class GraphicsState
     /**
      * @param Matrix|null $ctm
      */
-    public function __construct(Matrix $ctm = null)
+    public function __construct($ctm = null)
     {
         if ($ctm === null) {
             $ctm = new Matrix();
+        } elseif (!($ctm instanceof Matrix)) {
+            throw new \InvalidArgumentException('$ctm must be an instance of Fpdi\\Matrix or null');
         }
 
         $this->ctm = $ctm;
diff --git a/src/PdfParser/Type/PdfDictionary.php b/src/PdfParser/Type/PdfDictionary.php
index 8991322..9859afc 100644
--- a/src/PdfParser/Type/PdfDictionary.php
+++ b/src/PdfParser/Type/PdfDictionary.php
@@ -107,8 +107,11 @@ public static function create(array $entries = [])
      * @return PdfNull|PdfType
      * @throws PdfTypeException
      */
-    public static function get($dictionary, $key, PdfType $default = null)
+    public static function get($dictionary, $key, $default = null)
     {
+        if ($default !== null && !($default instanceof PdfType)) {
+            throw new \InvalidArgumentException('Default value must be an instance of PdfType or null');
+        }
         $dictionary = self::ensure($dictionary);
 
         if (isset($dictionary->value[$key])) {
diff --git a/src/PdfParser/Type/PdfStream.php b/src/PdfParser/Type/PdfStream.php
index cfa2cdb..a23fd0d 100644
--- a/src/PdfParser/Type/PdfStream.php
+++ b/src/PdfParser/Type/PdfStream.php
@@ -31,12 +31,15 @@ class PdfStream extends PdfType
      *
      * @param PdfDictionary $dictionary
      * @param StreamReader $reader
-     * @param PdfParser $parser Optional to keep backwards compatibility
+     * @param PdfParser|null $parser Optional to keep backwards compatibility
      * @return self
      * @throws PdfTypeException
      */
-    public static function parse(PdfDictionary $dictionary, StreamReader $reader, PdfParser $parser = null)
+    public static function parse(PdfDictionary $dictionary, StreamReader $reader, $parser = null)
     {
+        if ($parser !== null && !($parser instanceof PdfParser)) {
+            throw new \InvalidArgumentException('$parser must be an instance of PdfParser or null');
+        }
         $v = new self();
         $v->value = $dictionary;
         $v->reader = $reader;