diff --git a/src/ArrayTrait.php b/src/ArrayTrait.php
index d8768471..e778942b 100755
--- a/src/ArrayTrait.php
+++ b/src/ArrayTrait.php
@@ -44,7 +44,7 @@ public function __unset($name) {
      * @param string $value
      * @ignore
      */
-    public function offsetSet($offset, $value)
+    public function offsetSet(mixed $offset, mixed $value): void
     {
 
         if (is_callable([$this, 'set' . $offset])) {
@@ -58,7 +58,7 @@ public function offsetSet($offset, $value)
      * @return bool
      * @ignore
      */
-    public function offsetExists($offset)
+    public function offsetExists(mixed $offset): bool
     {
         return is_callable([$this, 'get' . $offset]) ||
             is_callable([$this, 'set' . $offset]) ||
@@ -69,7 +69,7 @@ public function offsetExists($offset)
      * @param string $offset
      * @ignore
      */
-    public function offsetUnset($offset)
+    public function offsetUnset(mixed $offset): void
     {
 
         if (is_callable([$this, 'set' . $offset])) {
@@ -83,7 +83,7 @@ public function offsetUnset($offset)
      * @return mixed|null
      * @ignore
      */
-    public function offsetGet($offset)
+    public function offsetGet(mixed $offset): mixed
     {
 
         if (is_callable([$this, 'get' . $offset])) {
@@ -116,4 +116,4 @@ public function offsetGet($offset)
 
         return null;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Element.php b/src/Element.php
index 4983effd..6cd043b9 100755
--- a/src/Element.php
+++ b/src/Element.php
@@ -613,7 +613,7 @@ public function getAst()
      * @return stdClass
      * @ignore
      */
-    public function jsonSerialize () {
+    public function jsonSerialize (): mixed {
 
         return $this->getAst();
     }
@@ -652,4 +652,4 @@ public function toObject()
     {
        return $this->ast;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Element/AtRule.php b/src/Element/AtRule.php
index 36a7786a..3b6034ab 100755
--- a/src/Element/AtRule.php
+++ b/src/Element/AtRule.php
@@ -100,7 +100,7 @@ public function addDeclaration ($name, $value) {
      * @return \stdClass
      * @ignore
      */
-    public function jsonSerialize () {
+    public function jsonSerialize (): mixed {
 
         $ast = parent::jsonSerialize();
 
@@ -116,4 +116,4 @@ public function jsonSerialize () {
 
         return $ast;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Element/NestingRule.php b/src/Element/NestingRule.php
index c9995c77..18c95d7c 100755
--- a/src/Element/NestingRule.php
+++ b/src/Element/NestingRule.php
@@ -10,9 +10,9 @@ class NestingRule extends Rule
     /**
      * @inheritDoc
      */
-    public function support(ElementInterface $child)
+    public function support(ElementInterface $child): bool
     {
 
         return true;
     }
-}
\ No newline at end of file
+}
diff --git a/src/Element/RuleList.php b/src/Element/RuleList.php
index 540e5bd6..93fd6f03 100755
--- a/src/Element/RuleList.php
+++ b/src/Element/RuleList.php
@@ -281,9 +281,9 @@ public function remove(ElementInterface $element)
      * return an iterator of child nodes
      * @return ArrayIterator|Traversable
      */
-    public function getIterator()
+    public function getIterator(): \Traversable
     {
 
         return new ArrayIterator($this->ast->children ?? []);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Parser/AccessTrait.php b/src/Parser/AccessTrait.php
index b7b3c8b2..190a54fd 100755
--- a/src/Parser/AccessTrait.php
+++ b/src/Parser/AccessTrait.php
@@ -52,8 +52,8 @@ public function __clone() {
     /**
      * @return array
      */
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         return get_object_vars($this);
     }
-}
\ No newline at end of file
+}
diff --git a/src/Property/PropertyList.php b/src/Property/PropertyList.php
index d9fde4bf..041fdd2e 100755
--- a/src/Property/PropertyList.php
+++ b/src/Property/PropertyList.php
@@ -360,7 +360,7 @@ public function isEmpty() {
     /**
      * @inheritDoc
      */
-    public function getIterator()
+    public function getIterator(): \Traversable
     {
         return $this->getProperties();
     }
diff --git a/src/Value.php b/src/Value.php
index c5050752..fad6084d 100755
--- a/src/Value.php
+++ b/src/Value.php
@@ -581,13 +581,13 @@ public static function parse($string, $property = null, bool $capture_whitespace
             return $string;
         }
 
-        if (trim($property) === '') {
+        if (trim((string)$property) === '') {
 
             $property = null;
         }
 
         $string = trim($string);
-        $property = strtolower($property);
+        $property = strtolower((string)$property);
 
         if ($property !== '') {
 
@@ -1466,8 +1466,8 @@ public function __toString()
         return $this->render();
     }
 
-    public function jsonSerialize()
+    public function jsonSerialize(): mixed
     {
         return $this->render();
     }
-}
\ No newline at end of file
+}