diff --git a/phpseclib/File/X509.php b/phpseclib/File/X509.php
index f3ee8137..df7b6033 100644
--- a/phpseclib/File/X509.php
+++ b/phpseclib/File/X509.php
@@ -2092,7 +2092,7 @@ class X509
      *
      * If $date isn't defined it is assumed to be the current date.
      *
-     * @param int $date optional
+     * @param \DateTime|string $date optional
      * @access public
      */
     function validateDate($date = null)
@@ -2102,7 +2102,7 @@ class X509
         }
 
         if (!isset($date)) {
-            $date = new DateTime($date, new DateTimeZone(@date_default_timezone_get()));
+            $date = new DateTime(null, new DateTimeZone(@date_default_timezone_get()));
         }
 
         $notBefore = $this->currentCert['tbsCertificate']['validity']['notBefore'];
@@ -2111,6 +2111,14 @@ class X509
         $notAfter = $this->currentCert['tbsCertificate']['validity']['notAfter'];
         $notAfter = isset($notAfter['generalTime']) ? $notAfter['generalTime'] : $notAfter['utcTime'];
 
+        switch (true) {
+            case is_string($date):
+                $date = new DateTime($date, new DateTimeZone(@date_default_timezone_get()));
+            default:
+                $notBefore = new DateTime($notBefore, new DateTimeZone(@date_default_timezone_get()));
+                $notAfter = new DateTime($notAfter, new DateTimeZone(@date_default_timezone_get()));
+        }
+
         switch (true) {
             case $date < new DateTime($notBefore, new DateTimeZone(@date_default_timezone_get())):
             case $date > new DateTime($notAfter, new DateTimeZone(@date_default_timezone_get())):