diff --git a/src/Generator/UnixTimeGenerator.php b/src/Generator/UnixTimeGenerator.php
index 93320cb..024ed51 100644
--- a/src/Generator/UnixTimeGenerator.php
+++ b/src/Generator/UnixTimeGenerator.php
@@ -19,6 +19,7 @@ use DateTimeImmutable;
 use DateTimeInterface;
 use Ramsey\Uuid\Type\Hexadecimal;
 
+use function assert;
 use function hash;
 use function pack;
 use function str_pad;
@@ -81,7 +82,8 @@ class UnixTimeGenerator implements TimeGeneratorInterface
             $time = str_pad(BigInteger::of($time)->toBytes(false), 6, "\x00", STR_PAD_LEFT);
         }
 
-        /** @var non-empty-string */
+        assert(strlen($time) === 6);
+
         return $time . pack('n*', self::$rand[1], self::$rand[2], self::$rand[3], self::$rand[4], self::$rand[5]);
     }
 
diff --git a/tests/Generator/UnixTimeGeneratorTest.php b/tests/Generator/UnixTimeGeneratorTest.php
index 8fab598..1d28d82 100644
--- a/tests/Generator/UnixTimeGeneratorTest.php
+++ b/tests/Generator/UnixTimeGeneratorTest.php
@@ -35,7 +35,11 @@ class UnixTimeGeneratorTest extends TestCase
 
         $bytes = $unixTimeGenerator->generate(null, null, $dateTime);
 
-        $this->assertSame($expectedBytes, $bytes);
+        $this->assertSame(
+            $expectedBytes,
+            $bytes,
+            'Failed asserting that "' . bin2hex($bytes) . '" is equal to "' . bin2hex($expectedBytes) . '"',
+        );
     }
 
     /**