diff --git a/common/framework/DateTime.php b/common/framework/DateTime.php
index 9f24cf0ae..b74bffec9 100644
--- a/common/framework/DateTime.php
+++ b/common/framework/DateTime.php
@@ -28,11 +28,11 @@ class DateTime
 	{
 		if ($format === self::FORMAT_RELATIVE)
 		{
-			return self::getRelativeTimestamp($timestamp ?: time());
+			return self::getRelativeTimestamp($timestamp ?? time());
 		}
 
-		$offset = Config::get('locale.internal_timezone') ?: date('Z', $timestamp);
-		return gmdate($format, ($timestamp ?: time()) + $offset);
+		$offset = Config::get('locale.internal_timezone') ?: date('Z', $timestamp ?? time());
+		return gmdate($format, ($timestamp ?? time()) + $offset);
 	}
 
 	/**
@@ -46,7 +46,7 @@ class DateTime
 	{
 		if ($format === self::FORMAT_RELATIVE)
 		{
-			return self::getRelativeTimestamp($timestamp ?: time());
+			return self::getRelativeTimestamp($timestamp ?? time());
 		}
 
 		$timezone = self::getTimezoneForCurrentUser();
@@ -55,7 +55,7 @@ class DateTime
 			self::$_timezones[$timezone] = new \DateTimeZone($timezone);
 		}
 		$datetime = new \DateTime();
-		$datetime->setTimestamp($timestamp ?: time());
+		$datetime->setTimestamp($timestamp ?? time());
 		$datetime->setTimezone(self::$_timezones[$timezone]);
 		return $datetime->format($format);
 	}
@@ -123,7 +123,7 @@ class DateTime
 			self::$_timezones[$timezone] = new \DateTimeZone($timezone);
 		}
 		$datetime = new \DateTime();
-		$datetime->setTimestamp($timestamp ?: time());
+		$datetime->setTimestamp($timestamp ?? time());
 		$datetime->setTimezone(self::$_timezones[$timezone]);
 		return $datetime->getOffset();
 	}
@@ -137,7 +137,7 @@ class DateTime
 	 */
 	public static function getTimezoneOffsetFromInternal(string $timezone, ?int $timestamp = null): int
 	{
-		return self::getTimezoneOffset($timezone, $timestamp ?: time()) - Config::get('locale.internal_timezone');
+		return self::getTimezoneOffset($timezone, $timestamp ?? time()) - Config::get('locale.internal_timezone');
 	}
 
 	/**
@@ -192,7 +192,7 @@ class DateTime
 	 */
 	public static function getRelativeTimestamp(?int $timestamp = null): string
 	{
-		$diff = \RX_TIME - intval($timestamp ?: time());
+		$diff = \RX_TIME - intval($timestamp ?? time());
 		$langs = lang('common.time_gap');
 
 		if ($diff < 3)
diff --git a/tests/unit/framework/DateTimeTest.php b/tests/unit/framework/DateTimeTest.php
index 036aa8f6e..3da9ccfbd 100644
--- a/tests/unit/framework/DateTimeTest.php
+++ b/tests/unit/framework/DateTimeTest.php
@@ -113,6 +113,18 @@ class DateTimeTest extends \Codeception\Test\Unit
 		Rhymix\Framework\Config::set('locale.internal_timezone', 32400);
 		$this->assertEquals($expected, zdate('19600419', 'Y-m-d H:i:s'));
 
+		// Test special dates.
+		Rhymix\Framework\Config::set('locale.internal_timezone', 32400);
+		$expected = '1970-01-01 09:00:00';
+		$this->assertEquals($expected, zdate('19700101', 'Y-m-d H:i:s'));
+		$expected = '1969-12-31 15:00:00';
+		$this->assertEquals($expected, zdate('1969-12-31 15:00:00', 'Y-m-d H:i:s'));
+		Rhymix\Framework\Config::set('locale.internal_timezone', 10800);
+		$expected = '1970-01-01 06:00:00';
+		$this->assertEquals($expected, zdate('19700101000000', 'Y-m-d H:i:s'));
+		$expected = '1970-01-01 00:00:00';
+		$this->assertEquals($expected, zdate('19691231180000', 'Y-m-d H:i:s'));
+
 		// Restore the internal timezone.
 		Rhymix\Framework\Config::set('locale.internal_timezone', 10800);
 	}