diff --git a/mqtt_sniffer.py b/mqtt_sniffer.py
index 6a4a54d..a52d865 100644
--- a/mqtt_sniffer.py
+++ b/mqtt_sniffer.py
@@ -130,7 +130,10 @@ class MqttSniffer(App):
         """Event handler called when a button is pressed."""
         if event.button.id == "send_button":
             if self.mqtt is not None:
-                self.mqtt.send(self.send_topic, self.send_payload)
+                if len(self.send_topic) > 0:
+                    self.mqtt.send(self.send_topic, self.send_payload)
+                else:
+                    logger.warning("Can't send mqtt message with empty topic. topic=%s; payload=%s", repr(self.send_topic), repr(self.send_payload))
 
 
 if __name__ == "__main__":