diff --git a/lib/ssh.php b/lib/ssh.php
index 6948645..14e771f 100644
--- a/lib/ssh.php
+++ b/lib/ssh.php
@@ -42,6 +42,13 @@ class OC_User_SSH extends \OCA\user_external\Base {
 	 * @return true/false
 	 */
 	public function checkPassword($uid, $password) {
+    if (!extension_loaded('ssh2')) {
+      OC::$server->getLogger()->error(
+        'ERROR: php-ssh2 PECL module missing',
+        ['app' => 'user_external']
+      );
+      return false;
+    }
 		$connection = ssh2_connect($this->host, $this->port);
 		if (ssh2_auth_password($connection, $uid, $password)) {
 			$this->storeUser($uid);