diff --git a/src/Query/TcpTransportExecutor.php b/src/Query/TcpTransportExecutor.php
index d940da61..c3900e4f 100644
--- a/src/Query/TcpTransportExecutor.php
+++ b/src/Query/TcpTransportExecutor.php
@@ -135,7 +135,7 @@ class TcpTransportExecutor implements ExecutorInterface
      * @param string         $nameserver
      * @param ?LoopInterface $loop
      */
-    public function __construct($nameserver, LoopInterface $loop = null)
+    public function __construct($nameserver, ?LoopInterface $loop = null)
     {
         if (\strpos($nameserver, '[') === false && \substr_count($nameserver, ':') >= 2 && \strpos($nameserver, '://') === false) {
             // several colons, but not enclosed in square brackets => enclose IPv6 address in square brackets
diff --git a/src/Query/TimeoutExecutor.php b/src/Query/TimeoutExecutor.php
index d6a63211..6559c52e 100644
--- a/src/Query/TimeoutExecutor.php
+++ b/src/Query/TimeoutExecutor.php
@@ -12,7 +12,12 @@ final class TimeoutExecutor implements ExecutorInterface
     private $loop;
     private $timeout;
 
-    public function __construct(ExecutorInterface $executor, $timeout, LoopInterface $loop = null)
+    /**
+     * @param ?ExecutorInterface $executor
+     * @param float|int $timeout
+     * @param ?LoopInterface $loop
+     */
+    public function __construct(?ExecutorInterface $executor, $timeout, ?LoopInterface $loop = null)
     {
         $this->executor = $executor;
         $this->loop = $loop ?: Loop::get();
diff --git a/src/Query/UdpTransportExecutor.php b/src/Query/UdpTransportExecutor.php
index 31290284..d1cb86e2 100644
--- a/src/Query/UdpTransportExecutor.php
+++ b/src/Query/UdpTransportExecutor.php
@@ -99,7 +99,7 @@ final class UdpTransportExecutor implements ExecutorInterface
      * @param string         $nameserver
      * @param ?LoopInterface $loop
      */
-    public function __construct($nameserver, LoopInterface $loop = null)
+    public function __construct($nameserver, ?LoopInterface $loop = null)
     {
         if (\strpos($nameserver, '[') === false && \substr_count($nameserver, ':') >= 2 && \strpos($nameserver, '://') === false) {
             // several colons, but not enclosed in square brackets => enclose IPv6 address in square brackets
diff --git a/src/Resolver/Factory.php b/src/Resolver/Factory.php
index 5fe608cb..eedebe1a 100644
--- a/src/Resolver/Factory.php
+++ b/src/Resolver/Factory.php
@@ -36,7 +36,7 @@ final class Factory
      * @throws \InvalidArgumentException for invalid DNS server address
      * @throws \UnderflowException when given DNS Config object has an empty list of nameservers
      */
-    public function create($config, LoopInterface $loop = null)
+    public function create($config, ?LoopInterface $loop = null)
     {
         $executor = $this->decorateHostsFileExecutor($this->createExecutor($config, $loop ?: Loop::get()));
 
@@ -59,7 +59,7 @@ public function create($config, LoopInterface $loop = null)
      * @throws \InvalidArgumentException for invalid DNS server address
      * @throws \UnderflowException when given DNS Config object has an empty list of nameservers
      */
-    public function createCached($config, LoopInterface $loop = null, CacheInterface $cache = null)
+    public function createCached($config, ?LoopInterface $loop = null, ?CacheInterface $cache = null)
     {
         // default to keeping maximum of 256 responses in cache unless explicitly given
         if (!($cache instanceof CacheInterface)) {