diff --git a/src/pocketmine/scheduler/AsyncPool.php b/src/pocketmine/scheduler/AsyncPool.php
index cb7b1a5fa..4d722f2d5 100644
--- a/src/pocketmine/scheduler/AsyncPool.php
+++ b/src/pocketmine/scheduler/AsyncPool.php
@@ -24,6 +24,7 @@ declare(strict_types=1);
 namespace pocketmine\scheduler;
 
 use pocketmine\Server;
+use pocketmine\utils\Utils;
 
 /**
  * Manages general-purpose worker threads used for processing asynchronous tasks, and the tasks submitted to those
@@ -96,6 +97,7 @@ class AsyncPool{
 	 * @param \Closure $hook
 	 */
 	public function addWorkerStartHook(\Closure $hook) : void{
+		Utils::validateCallableSignature(function(int $worker) : void{}, $hook);
 		$this->workerStartHooks[spl_object_hash($hook)] = $hook;
 		foreach($this->workers as $i => $worker){
 			$hook($i);
diff --git a/src/pocketmine/scheduler/ClosureTask.php b/src/pocketmine/scheduler/ClosureTask.php
index 8ada271ff..f023173d4 100644
--- a/src/pocketmine/scheduler/ClosureTask.php
+++ b/src/pocketmine/scheduler/ClosureTask.php
@@ -45,6 +45,7 @@ class ClosureTask extends Task{
 	 * @param \Closure $closure Must accept only ONE parameter, $currentTick
 	 */
 	public function __construct(\Closure $closure){
+		Utils::validateCallableSignature(function(int $currentTick) : void{}, $closure);
 		$this->closure = $closure;
 	}