diff --git a/includes/CategoryTree.php b/includes/CategoryTree.php
index 90c6a10c..077a938a 100644
--- a/includes/CategoryTree.php
+++ b/includes/CategoryTree.php
@@ -294,7 +294,7 @@ class CategoryTree {
 	 * Returns a string with a HTML represenation of the given page.
 	 * $info must be an associative array, containing at least a Title object under the 'title' key.
 	 */
-	public function renderNodeInfo( Title $title, Category $cat = null, int $children = 0 ): string {
+	public function renderNodeInfo( Title $title, ?Category $cat = null, int $children = 0 ): string {
 		$mode = $this->optionManager->getOption( 'mode' );
 
 		$isInCatNS = $title->inNamespace( NS_CATEGORY );
diff --git a/includes/Hooks.php b/includes/Hooks.php
index 737964a5..805ccf4a 100644
--- a/includes/Hooks.php
+++ b/includes/Hooks.php
@@ -190,8 +190,8 @@ class Hooks implements
 	public function parserHook(
 		$cat,
 		array $argv,
-		Parser $parser = null,
-		PPFrame $frame = null
+		?Parser $parser = null,
+		?PPFrame $frame = null
 	) {
 		if ( $parser ) {
 			$parserOutput = $parser->getOutput();
diff --git a/includes/OptionManager.php b/includes/OptionManager.php
index 7416e23c..97eafa02 100644
--- a/includes/OptionManager.php
+++ b/includes/OptionManager.php
@@ -260,7 +260,7 @@ class OptionManager {
 	 * @param int|null $depth
 	 * @return string
 	 */
-	public function getOptionsAsCacheKey( int $depth = null ): string {
+	public function getOptionsAsCacheKey( ?int $depth = null ): string {
 		$key = '';
 
 		foreach ( $this->mOptions as $k => $v ) {
@@ -280,7 +280,7 @@ class OptionManager {
 	 * @param int|null $depth
 	 * @return mixed
 	 */
-	public function getOptionsAsJsStructure( int $depth = null ) {
+	public function getOptionsAsJsStructure( ?int $depth = null ) {
 		$opt = $this->mOptions;
 		if ( $depth !== null ) {
 			$opt['depth'] = $depth;