diff --git a/src/block/Banner.php b/src/block/Banner.php
index 9091d5bfb..9bf16b9fd 100644
--- a/src/block/Banner.php
+++ b/src/block/Banner.php
@@ -138,7 +138,7 @@ class Banner extends Transparent{
 	 * @phpstan-param Deque<BannerPattern> $patterns
 	 */
 	public function setPatterns(Deque $patterns) : void{
-		$checked = $patterns->filter(function($v){ return $v instanceof BannerPattern; });
+		$checked = $patterns->filter(function($v) : bool{ return $v instanceof BannerPattern; });
 		if($checked->count() !== $patterns->count()){
 			throw new \TypeError("Deque must only contain " . BannerPattern::class . " objects");
 		}
diff --git a/src/inventory/CallbackInventoryChangeListener.php b/src/inventory/CallbackInventoryChangeListener.php
index e16e01501..388b9bf1b 100644
--- a/src/inventory/CallbackInventoryChangeListener.php
+++ b/src/inventory/CallbackInventoryChangeListener.php
@@ -46,10 +46,10 @@ class CallbackInventoryChangeListener implements InventoryChangeListener{
 	 */
 	public function __construct(?\Closure $onSlotChange, ?\Closure $onContentChange){
 		if($onSlotChange !== null){
-			Utils::validateCallableSignature(function(Inventory $inventory, int $slot){}, $onSlotChange);
+			Utils::validateCallableSignature(function(Inventory $inventory, int $slot) : void{}, $onSlotChange);
 		}
 		if($onContentChange !== null){
-			Utils::validateCallableSignature(function(Inventory $inventory){}, $onContentChange);
+			Utils::validateCallableSignature(function(Inventory $inventory) : void{}, $onContentChange);
 		}
 
 		$this->onSlotChangeCallback = $onSlotChange;
diff --git a/src/network/mcpe/NetworkSession.php b/src/network/mcpe/NetworkSession.php
index 5b3725043..27ddf11b2 100644
--- a/src/network/mcpe/NetworkSession.php
+++ b/src/network/mcpe/NetworkSession.php
@@ -740,7 +740,7 @@ class NetworkSession{
 	 * @phpstan-param \Closure(int $chunkX, int $chunkZ) : void $onCompletion
 	 */
 	public function startUsingChunk(int $chunkX, int $chunkZ, \Closure $onCompletion) : void{
-		Utils::validateCallableSignature(function(int $chunkX, int $chunkZ){}, $onCompletion);
+		Utils::validateCallableSignature(function(int $chunkX, int $chunkZ) : void{}, $onCompletion);
 
 		$world = $this->player->getLocation()->getWorld();
 		assert($world !== null);
@@ -797,7 +797,7 @@ class NetworkSession{
 	}
 
 	public function syncPlayerList() : void{
-		$this->sendDataPacket(PlayerListPacket::add(array_map(function(Player $player){
+		$this->sendDataPacket(PlayerListPacket::add(array_map(function(Player $player) : PlayerListEntry{
 			return PlayerListEntry::createAdditionEntry($player->getUniqueId(), $player->getId(), $player->getDisplayName(), SkinAdapterSingleton::get()->toSkinData($player->getSkin()), $player->getXuid());
 		}, $this->server->getOnlinePlayers())));
 	}
diff --git a/src/network/mcpe/compression/CompressBatchPromise.php b/src/network/mcpe/compression/CompressBatchPromise.php
index 94909d5fd..8fa8b12ae 100644
--- a/src/network/mcpe/compression/CompressBatchPromise.php
+++ b/src/network/mcpe/compression/CompressBatchPromise.php
@@ -45,7 +45,7 @@ class CompressBatchPromise{
 	public function onResolve(\Closure ...$callbacks) : void{
 		$this->checkCancelled();
 		foreach($callbacks as $callback){
-			Utils::validateCallableSignature(function(CompressBatchPromise $promise){}, $callback);
+			Utils::validateCallableSignature(function(CompressBatchPromise $promise) : void{}, $callback);
 		}
 		if($this->result !== null){
 			foreach($callbacks as $callback){
diff --git a/src/network/mcpe/handler/ResourcePacksPacketHandler.php b/src/network/mcpe/handler/ResourcePacksPacketHandler.php
index 1f79bf988..51ec66cba 100644
--- a/src/network/mcpe/handler/ResourcePacksPacketHandler.php
+++ b/src/network/mcpe/handler/ResourcePacksPacketHandler.php
@@ -63,7 +63,7 @@ class ResourcePacksPacketHandler extends PacketHandler{
 	}
 
 	public function setUp() : void{
-		$resourcePackEntries = array_map(static function(ResourcePack $pack){
+		$resourcePackEntries = array_map(static function(ResourcePack $pack) : ResourcePackInfoEntry{
 			//TODO: more stuff
 			return new ResourcePackInfoEntry($pack->getPackId(), $pack->getPackVersion(), $pack->getPackSize(), "", "", "", false);
 		}, $this->resourcePackManager->getResourceStack());
@@ -109,7 +109,7 @@ class ResourcePacksPacketHandler extends PacketHandler{
 
 				break;
 			case ResourcePackClientResponsePacket::STATUS_HAVE_ALL_PACKS:
-				$stack = array_map(static function(ResourcePack $pack){
+				$stack = array_map(static function(ResourcePack $pack) : ResourcePackStackEntry{
 					return new ResourcePackStackEntry($pack->getPackId(), $pack->getPackVersion(), ""); //TODO: subpacks
 				}, $this->resourcePackManager->getResourceStack());
 
diff --git a/src/network/mcpe/protocol/types/command/CommandData.php b/src/network/mcpe/protocol/types/command/CommandData.php
index 5b3ec8fe0..e528fb50a 100644
--- a/src/network/mcpe/protocol/types/command/CommandData.php
+++ b/src/network/mcpe/protocol/types/command/CommandData.php
@@ -41,9 +41,9 @@ class CommandData{
 	 * @param CommandParameter[][] $overloads
 	 */
 	public function __construct(string $name, string $description, int $flags, int $permission, ?CommandEnum $aliases, array $overloads){
-		(function(array ...$overloads){
+		(function(array ...$overloads) : void{
 			foreach($overloads as $overload){
-				(function(CommandParameter ...$parameters){})(...$overload);
+				(function(CommandParameter ...$parameters) : void{})(...$overload);
 			}
 		})(...$overloads);
 		$this->name = $name;
diff --git a/src/plugin/ApiVersion.php b/src/plugin/ApiVersion.php
index be2d2ca07..2cf11a722 100644
--- a/src/plugin/ApiVersion.php
+++ b/src/plugin/ApiVersion.php
@@ -93,8 +93,8 @@ final class ApiVersion{
 			}
 		}
 
-		usort($result, static function(VersionString $string1, VersionString $string2){ return $string1->compare($string2); });
+		usort($result, static function(VersionString $string1, VersionString $string2) : int{ return $string1->compare($string2); });
 
-		return array_map(static function(VersionString $string){ return $string->getBaseVersion(); }, $result);
+		return array_map(static function(VersionString $string) : string{ return $string->getBaseVersion(); }, $result);
 	}
 }
diff --git a/src/scheduler/ClosureTask.php b/src/scheduler/ClosureTask.php
index 6152469c0..2a9996de1 100644
--- a/src/scheduler/ClosureTask.php
+++ b/src/scheduler/ClosureTask.php
@@ -49,7 +49,7 @@ class ClosureTask extends Task{
 	 * @phpstan-param \Closure(int) : void $closure
 	 */
 	public function __construct(\Closure $closure){
-		Utils::validateCallableSignature(function(int $currentTick){}, $closure);
+		Utils::validateCallableSignature(function(int $currentTick) : void{}, $closure);
 		$this->closure = $closure;
 	}
 
diff --git a/src/scheduler/SendUsageTask.php b/src/scheduler/SendUsageTask.php
index d943efb6c..4b12b26c7 100644
--- a/src/scheduler/SendUsageTask.php
+++ b/src/scheduler/SendUsageTask.php
@@ -124,7 +124,7 @@ class SendUsageTask extends AsyncTask{
 					$playerList[$k] = md5($v);
 				}
 
-				$players = array_map(function(Player $p){ return md5($p->getUniqueId()->toBinary()); }, $server->getOnlinePlayers());
+				$players = array_map(function(Player $p) : string{ return md5($p->getUniqueId()->toBinary()); }, $server->getOnlinePlayers());
 
 				$data["players"] = [
 					"count" => count($players),
diff --git a/src/world/utils/SubChunkIteratorManager.php b/src/world/utils/SubChunkIteratorManager.php
index 6187f367e..453093017 100644
--- a/src/world/utils/SubChunkIteratorManager.php
+++ b/src/world/utils/SubChunkIteratorManager.php
@@ -90,7 +90,7 @@ class SubChunkIteratorManager{
 	 * @phpstan-param \Closure() : void $callback
 	 */
 	public function onSubChunkChange(\Closure $callback) : void{
-		Utils::validateCallableSignature(function(){}, $callback);
+		Utils::validateCallableSignature(function() : void{}, $callback);
 		$this->onSubChunkChangeFunc = $callback;
 	}