diff --git a/src/world/biome/model/BiomeDefinitionEntryData.php b/src/world/biome/model/BiomeDefinitionEntryData.php
index 8a5c3d354..bb63b36e1 100644
--- a/src/world/biome/model/BiomeDefinitionEntryData.php
+++ b/src/world/biome/model/BiomeDefinitionEntryData.php
@@ -28,7 +28,7 @@ namespace pocketmine\world\biome\model;
  */
 final class BiomeDefinitionEntryData{
 	/** @required */
-	public ?int $id;
+	public int $id;
 
 	/** @required */
 	public float $temperature;