diff --git a/src/Ulid.php b/src/Ulid.php
index 86ac5fe..0590d8d 100644
--- a/src/Ulid.php
+++ b/src/Ulid.php
@@ -24,11 +24,6 @@ class Ulid
 {
     const ENCODING_CHARS = '0123456789ABCDEFGHJKMNPQRSTVWXYZ';
     const ENCODING_LENGTH = 32;
-    /**
-     * Last generated timestamp.
-     * @var int
-     */
-    private static $lastTime = 0;
 
     /**
      * Generate a new ULID.
@@ -39,16 +34,7 @@ class Ulid
 
     public static function generate(bool $upperCase = true): string
     {
-        $time      = (int)(microtime(true) * 1000);
-
-        // If the current timestamp is equal or less than the last generated one,
-        // increase it by one millisecond to ensure ULIDs are always sorted correctly.
-        if ($time <= self::$lastTime) {
-            $time = self::$lastTime + 1;
-        }
-
-        self::$lastTime = $time;
-
+        $time      = (int)(microtime(true) * 1000000);
         $timeChars = self::encodeTime($time);
         $randChars = self::encodeRandomness();
         $ulid      = $timeChars . $randChars;
diff --git a/tests/unit/UlidTest.php b/tests/unit/UlidTest.php
index 7820e81..7c20ec5 100644
--- a/tests/unit/UlidTest.php
+++ b/tests/unit/UlidTest.php
@@ -9,7 +9,7 @@ class UlidTest extends \PHPUnit\Framework\TestCase
      * Sets up the fixture, for example, opens a network connection.
      * This method is called before a test is executed.
      */
-    protected function setUp()
+    protected function setUp(): void
     {
     }
 
@@ -17,7 +17,7 @@ protected function setUp()
      * Tears down the fixture, for example, closes a network connection.
      * This method is called after a test is executed.
      */
-    protected function tearDown()
+    protected function tearDown(): void
     {
     }
 
@@ -26,15 +26,18 @@ protected function tearDown()
      */
     public function testGenerate()
     {
-        $ulid = Ulid::generate();
+        $ulid1 = Ulid::generate();
+        usleep(2000);  // Wait for 2 milliseconds to ensure a different timestamp
+        $ulid2 = Ulid::generate();
 
-        $this->assertRegExp('/^[0-9A-Z]{26}$/', \strtoupper($ulid));
+        $this->assertNotEquals($ulid1, $ulid2, 'ULIDs should be unique');
+        $this->assertTrue(strcasecmp($ulid1, $ulid2) < 0, 'ULIDs should collate correctly');
     }
     public function testGeneratesLowercaseIdentifierWhenConfigured(): void
     {
         $ulid = Ulid::generate(false); //generate lower case
 
-        $this->assertRegExp('/[0-9][a-z]/', $ulid);
+        $this->assertMatchesRegularExpression('/[0-9][a-z]/', $ulid);
     }
 
     public function testGeneratesTwentySixChars(): void