diff --git a/opcua2mqtt/MqttBase.py b/opcua2mqtt/MqttBase.py
index 8649b68..7187cfe 100644
--- a/opcua2mqtt/MqttBase.py
+++ b/opcua2mqtt/MqttBase.py
@@ -46,7 +46,7 @@ class AbstractMqttPublisher(threading.Thread):
             )
         elif ("ca" in self.config):
             self.client.tls_set(
-                keyfile=self.config["key"],
+                ca_certs=self.config["ca"],
                 cert_reqs=ssl.CERT_REQUIRED,
                 tls_version=ssl.PROTOCOL_TLSv1_2, 
                 ciphers=None # this does not mean "no cipher" but it means "default ciphers"