diff --git a/core/src/command/mqtt.rs b/core/src/command/mqtt.rs
index 0e8098b..0401058 100644
--- a/core/src/command/mqtt.rs
+++ b/core/src/command/mqtt.rs
@@ -18,6 +18,7 @@ pub struct Config {
 pub enum Mode {
     Drogue {
         // allow overriding the application
+        #[serde(default)]
         application: Option<String>,
     },
 }