diff --git a/src/pocketmine/world/generator/Generator.php b/src/pocketmine/world/generator/Generator.php
index 0005138ac..0dd619cba 100644
--- a/src/pocketmine/world/generator/Generator.php
+++ b/src/pocketmine/world/generator/Generator.php
@@ -29,7 +29,7 @@ namespace pocketmine\world\generator;
 use pocketmine\utils\Random;
 use pocketmine\utils\Utils;
 use pocketmine\world\ChunkManager;
-use function ctype_digit;
+use function preg_match;
 
 abstract class Generator{
 
@@ -43,7 +43,7 @@ abstract class Generator{
 	public static function convertSeed(string $seed) : ?int{
 		if($seed === ""){ //empty seed should cause a random seed to be selected - can't use 0 here because 0 is a valid seed
 			$convertedSeed = null;
-		}elseif(ctype_digit($seed)){ //this avoids treating seeds like "404.4" as integer seeds
+		}elseif(preg_match('/^-?\d+$/', $seed) === 1){ //this avoids treating seeds like "404.4" as integer seeds
 			$convertedSeed = (int) $seed;
 		}else{
 			$convertedSeed = Utils::javaStringHash($seed);