diff --git a/src/Ulid.php b/src/Ulid.php
index 1d10b76..293ff52 100644
--- a/src/Ulid.php
+++ b/src/Ulid.php
@@ -67,6 +67,9 @@ public function getRandomString():string {
 
 	private function base32(int $number):string {
 		$skipCharacters = ["i", "l", "o", "u"];
+		if($number < 0) {
+			$number = -$number;
+		}
 		$converted = base_convert((string)$number, 10, 32);
 
 		for($i = 0, $len = strlen($converted); $i < $len; $i++) {
diff --git a/test/phpunit/UlidTest.php b/test/phpunit/UlidTest.php
index 696cd3e..4833631 100644
--- a/test/phpunit/UlidTest.php
+++ b/test/phpunit/UlidTest.php
@@ -51,7 +51,6 @@ public function testToString_containsNoAmbiguousCharacters():void {
 		for($i = 0; $i < 1_000; $i++) {
 			$sut = new Ulid();
 			foreach($skipCharacters as $char) {
-				echo $sut, PHP_EOL;
 				self::assertStringNotContainsString($char, $sut);
 			}
 		}
@@ -76,7 +75,6 @@ public function testConstruct_setTimestampLength():void {
 		for($i = 0; $i < 10; $i++) {
 			$tLength = rand(5, 10);
 			$sut = new Ulid(timestampLength: $tLength);
-			echo $sut, PHP_EOL;
 			$tString = $sut->getTimestampString();
 			self::assertSame($tLength, strlen($tString));
 		}