diff --git a/smtp.php b/smtp.php
index 077de87d..b329d4b0 100644
--- a/smtp.php
+++ b/smtp.php
@@ -352,7 +352,7 @@ function __construct(
 			'Content-Type'=>'text/plain; '.
 				'charset='.Base::instance()->ENCODING
 		];
-		$this->host=strtolower((($this->scheme=strtolower($scheme))=='ssl'?
+		$this->host=strtolower((($this->scheme=strtolower($scheme?:''))=='ssl'?
 			'ssl':'tcp').'://'.$host);
 		$this->port=$port;
 		$this->user=$user;