diff --git a/models/Session.php b/models/Session.php
index 13b38dc..648439e 100644
--- a/models/Session.php
+++ b/models/Session.php
@@ -15,15 +15,17 @@ class Session
 		// Resuming an existing session? Check what we know!
 		if (isset($_SESSION['user_id'], $_SESSION['ip_address'], $_SESSION['user_agent']))
 		{
-			if (isset($_SERVER['REMOTE_ADDR']) && $_SESSION['ip_address'] !== $_SERVER['REMOTE_ADDR'])
+			// If we're not browsing over HTTPS, protect against session hijacking.
+			if (!isset($_SERVER['HTTPS']) && isset($_SERVER['REMOTE_ADDR']) && $_SESSION['ip_address'] !== $_SERVER['REMOTE_ADDR'])
 			{
 				$_SESSION = [];
-				throw new NotAllowedException('Your session failed to validate: your IP address has changed. Please re-login and try again.');
+				throw new UserFacingException('Your session failed to validate: your IP address has changed. Please re-login and try again.');
 			}
+			// Either way, require re-login if the browser identifier has changed.
 			elseif (isset($_SERVER['HTTP_USER_AGENT']) && $_SESSION['user_agent'] !== $_SERVER['HTTP_USER_AGENT'])
 			{
 				$_SESSION = [];
-				throw new NotAllowedException('Your session failed to validate: your browser identifier has changed. Please re-login and try again.');
+				throw new UserFacingException('Your session failed to validate: your browser identifier has changed. Please re-login and try again.');
 			}
 		}
 		elseif (!isset($_SESSION['ip_address'], $_SESSION['user_agent']))
@@ -47,7 +49,7 @@ class Session
 		// First, check whether the submitted token and key match the ones in storage.
 		if (($method === 'post' && (!isset($_POST[$_SESSION['session_token_key']]) || $_POST[$_SESSION['session_token_key']] !== $_SESSION['session_token'])) ||
 			($method === 'get' && (!isset($_GET[$_SESSION['session_token_key']]) || $_GET[$_SESSION['session_token_key']] !== $_SESSION['session_token'])))
-			trigger_error('Session failed to verify (' . $method . '). Please reload the page and try again.', E_USER_ERROR);
+			throw new UserFacingException('Session failed to verify (' . $method . '). Please reload the page and try again.');
 
 		// Check the referring site, too -- should be the same site!
 		$referring_host = isset($_SERVER['HTTP_REFERER']) ? parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST) : '';
@@ -62,7 +64,7 @@ class Session
 
 			// The referring_host must match either the base_url_host or the current_host.
 			if (strtolower($referring_host) !== strtolower($base_url_host) && strtolower($referring_host) !== strtolower($current_host))
-				trigger_error('Invalid referring URL. Please reload the page and try again.', E_USER_ERROR);
+				throw new UserFacingException('Invalid referring URL. Please reload the page and try again.');
 		}
 
 		// All looks good from here! But you can only use this token once, so...