diff --git a/src/adapters/mqtt/index.ts b/src/adapters/mqtt/index.ts
index 3ba70ecca..95e428110 100644
--- a/src/adapters/mqtt/index.ts
+++ b/src/adapters/mqtt/index.ts
@@ -45,7 +45,7 @@ class MqttAdapter extends Adapter {
       this.client = mqtt.connect({
         host: url.host,
         port: url.port || (url.protocol === 'mqtt:' ? 1883 : 8883),
-        protocol: url.protocol.substr(0, url.protocol.length - 1),
+        protocol: url.protocol.slice(0, url.protocol.length - 1),
         clientId: serverBinding && serverBinding.clientId,
         clean: serverBinding && serverBinding.cleanSession,
         will: serverBinding && serverBinding.will && {