diff --git a/src/pocketmine/level/Level.php b/src/pocketmine/level/Level.php
index 69144cde5..b3066aa14 100644
--- a/src/pocketmine/level/Level.php
+++ b/src/pocketmine/level/Level.php
@@ -382,6 +382,7 @@ class Level implements ChunkManager, Metadatable{
 
 		$this->server->getLogger()->info($this->server->getLanguage()->translateString("pocketmine.level.preparing", [$this->displayName]));
 		$this->generator = GeneratorManager::getGenerator($this->provider->getGenerator());
+		//TODO: validate generator options
 
 		$this->folderName = $name;
 
diff --git a/src/pocketmine/level/generator/Flat.php b/src/pocketmine/level/generator/Flat.php
index 1efa82c33..153fb5783 100644
--- a/src/pocketmine/level/generator/Flat.php
+++ b/src/pocketmine/level/generator/Flat.php
@@ -33,10 +33,11 @@ use pocketmine\level\generator\populator\Ore;
 use pocketmine\level\generator\populator\Populator;
 use pocketmine\math\Vector3;
 use pocketmine\utils\Random;
+use function array_map;
 use function count;
 use function explode;
+use function preg_match;
 use function preg_match_all;
-use function str_replace;
 
 class Flat extends Generator{
 	/** @var Chunk */
@@ -62,6 +63,11 @@ class Flat extends Generator{
 		return "flat";
 	}
 
+	/**
+	 * @param array $options
+	 *
+	 * @throws InvalidGeneratorOptionsException
+	 */
 	public function __construct(array $options = []){
 		$this->options = $options;
 		if(isset($this->options["preset"]) and $this->options["preset"] != ""){
@@ -89,13 +95,28 @@ class Flat extends Generator{
 		}
 	}
 
+	/**
+	 * @param string $layers
+	 *
+	 * @return int[][]
+	 * @throws InvalidGeneratorOptionsException
+	 */
 	public static function parseLayers(string $layers) : array{
 		$result = [];
-		preg_match_all('#^(([0-9]*x|)([0-9]{1,3})(|:[0-9]{0,2}))$#m', str_replace(",", "\n", $layers), $matches);
+		$split = array_map('\trim', explode(',', $layers));
 		$y = 0;
-		foreach($matches[3] as $i => $b){
-			$b = ItemFactory::fromString($b . $matches[4][$i]);
-			$cnt = $matches[2][$i] === "" ? 1 : (int) $matches[2][$i];
+		foreach($split as $line){
+			preg_match('#^(?:(\d+)x)?(.+)$#', $line, $matches);
+			if(count($matches) !== 3){
+				throw new InvalidGeneratorOptionsException("Invalid preset layer \"$line\"");
+			}
+
+			$cnt = $matches[1] !== "" ? (int) $matches[1] : 1;
+			try{
+				$b = ItemFactory::fromString($matches[2])->getBlock();
+			}catch(\InvalidArgumentException $e){
+				throw new InvalidGeneratorOptionsException("Invalid preset layer \"$line\": " . $e->getMessage(), 0, $e);
+			}
 			for($cY = $y, $y += $cnt; $cY < $y; ++$cY){
 				$result[$cY] = [$b->getId(), $b->getDamage()];
 			}
@@ -113,6 +134,7 @@ class Flat extends Generator{
 
 		$this->floorLevel = count($this->structure);
 
+		//TODO: more error checking
 		preg_match_all('#(([0-9a-z_]{1,})\(?([0-9a-z_ =:]{0,})\)?),?#', $options, $matches);
 		foreach($matches[2] as $i => $option){
 			$params = true;
diff --git a/src/pocketmine/level/generator/Generator.php b/src/pocketmine/level/generator/Generator.php
index b72c0a7ce..dba5fa8a8 100644
--- a/src/pocketmine/level/generator/Generator.php
+++ b/src/pocketmine/level/generator/Generator.php
@@ -58,6 +58,11 @@ abstract class Generator{
 	/** @var Random */
 	protected $random;
 
+	/**
+	 * @param array $settings
+	 *
+	 * @throws InvalidGeneratorOptionsException
+	 */
 	abstract public function __construct(array $settings = []);
 
 
diff --git a/src/pocketmine/level/generator/InvalidGeneratorOptionsException.php b/src/pocketmine/level/generator/InvalidGeneratorOptionsException.php
new file mode 100644
index 000000000..9489589f0
--- /dev/null
+++ b/src/pocketmine/level/generator/InvalidGeneratorOptionsException.php
@@ -0,0 +1,28 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\level\generator;
+
+class InvalidGeneratorOptionsException extends \UnexpectedValueException{
+
+}
diff --git a/src/pocketmine/level/generator/hell/Nether.php b/src/pocketmine/level/generator/hell/Nether.php
index 2ec0d1fae..110d3687b 100644
--- a/src/pocketmine/level/generator/hell/Nether.php
+++ b/src/pocketmine/level/generator/hell/Nether.php
@@ -27,6 +27,7 @@ use pocketmine\block\Block;
 use pocketmine\level\biome\Biome;
 use pocketmine\level\ChunkManager;
 use pocketmine\level\generator\Generator;
+use pocketmine\level\generator\InvalidGeneratorOptionsException;
 use pocketmine\level\generator\noise\Simplex;
 use pocketmine\level\generator\populator\Populator;
 use pocketmine\math\Vector3;
@@ -51,6 +52,11 @@ class Nether extends Generator{
 	/** @var Simplex */
 	private $noiseBase;
 
+	/**
+	 * @param array $options
+	 *
+	 * @throws InvalidGeneratorOptionsException
+	 */
 	public function __construct(array $options = []){
 
 	}
diff --git a/src/pocketmine/level/generator/normal/Normal.php b/src/pocketmine/level/generator/normal/Normal.php
index f9e4d3d7a..cfb7ea65e 100644
--- a/src/pocketmine/level/generator/normal/Normal.php
+++ b/src/pocketmine/level/generator/normal/Normal.php
@@ -29,6 +29,7 @@ use pocketmine\level\biome\Biome;
 use pocketmine\level\ChunkManager;
 use pocketmine\level\generator\biome\BiomeSelector;
 use pocketmine\level\generator\Generator;
+use pocketmine\level\generator\InvalidGeneratorOptionsException;
 use pocketmine\level\generator\noise\Simplex;
 use pocketmine\level\generator\object\OreType;
 use pocketmine\level\generator\populator\GroundCover;
@@ -57,6 +58,11 @@ class Normal extends Generator{
 	private static $GAUSSIAN_KERNEL = null;
 	private static $SMOOTH_SIZE = 2;
 
+	/**
+	 * @param array $options
+	 *
+	 * @throws InvalidGeneratorOptionsException
+	 */
 	public function __construct(array $options = []){
 		if(self::$GAUSSIAN_KERNEL === null){
 			self::generateKernel();