diff --git a/src/SMTP.php b/src/SMTP.php
index 27b752ec3..eaaadffd9 100644
--- a/src/SMTP.php
+++ b/src/SMTP.php
@@ -443,14 +443,14 @@ public function authenticate(
                 return false;
             }
 
-            $this->edebug('Auth method requested: ' . ($authtype ? $authtype : 'UNKNOWN'), self::DEBUG_LOWLEVEL);
+            $this->edebug('Auth method requested: ' . ($authtype ? $authtype : 'UNSPECIFIED'), self::DEBUG_LOWLEVEL);
             $this->edebug(
                 'Auth methods available on the server: ' . implode(',', $this->server_caps['AUTH']),
                 self::DEBUG_LOWLEVEL
             );
 
             //If we have requested a specific auth type, check the server supports it before trying others
-            if (!in_array($authtype, $this->server_caps['AUTH'])) {
+            if (null !== $authtype and !in_array($authtype, $this->server_caps['AUTH'])) {
                 $this->edebug('Requested auth method not available: ' . $authtype, self::DEBUG_LOWLEVEL);
                 $authtype = null;
             }