diff --git a/src/main.rs b/src/main.rs
index 4fd644b..8650b71 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -25,8 +25,9 @@ use settings::Settings;
 /// Observability dashboard from terminal output.
 #[derive(Parser, Debug)]
 struct Args {
-    /// Port to serve the API and webapp on.
-    #[arg(long, default_value_t = 8420)]
+    /// Port to serve the API and webapp on. Defaults to 0, letting the OS assign
+    /// an ephemeral free port.
+    #[arg(long, default_value_t = 0)]
     port: u16,
 
     /// Directory containing the built webapp (index.html + assets).
@@ -91,10 +92,14 @@ async fn main() {
     let listener = TcpListener::bind(("0.0.0.0", args.port))
         .await
         .expect("failed to bind listener");
+    let bound_port = listener
+        .local_addr()
+        .expect("failed to read back bound address")
+        .port();
 
     eprintln!(
         "ottyl serving on http://localhost:{} (reading logs from stdin)",
-        args.port
+        bound_port
     );
 
     axum::serve(listener, app)