diff --git a/homeassistant/components/mqtt/__init__.py b/homeassistant/components/mqtt/__init__.py
index 90c89b3193d9a8..64e804d77151ee 100644
--- a/homeassistant/components/mqtt/__init__.py
+++ b/homeassistant/components/mqtt/__init__.py
@@ -315,6 +315,10 @@ def async_setup(hass, config):
         client_cert = conf.get(CONF_CLIENT_CERT)
         tls_insecure = conf.get(CONF_TLS_INSECURE)
         protocol = conf[CONF_PROTOCOL]
+
+        # hbmqtt requires a client id to be set.
+        if client_id is None:
+            client_id = 'home-assistant'
     elif broker_config:
         # If no broker passed in, auto config to internal server
         broker, port, username, password, certificate, protocol = broker_config