diff --git a/src/app.rs b/src/app.rs
index ec9fddc..569a798 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -41,10 +41,15 @@ pub struct Application {
     persistence: Persistence,
     viewports: HashMap<ViewportId, Viewport>,
     focused: Option<ViewportId>,
+    init_debug_port: Option<u16>,
 }
 
 impl Application {
-    pub fn new(client: EmulatorClient, proxy: EventLoopProxy<UserEvent>) -> Self {
+    pub fn new(
+        client: EmulatorClient,
+        proxy: EventLoopProxy<UserEvent>,
+        debug_port: Option<u16>,
+    ) -> Self {
         let icon = load_icon().ok().map(Arc::new);
         let persistence = Persistence::new();
         let mappings = MappingProvider::new(persistence.clone());
@@ -63,6 +68,7 @@ impl Application {
             persistence,
             viewports: HashMap::new(),
             focused: None,
+            init_debug_port: debug_port,
         }
     }
 
@@ -86,9 +92,12 @@ impl ApplicationHandler<UserEvent> for Application {
             self.persistence.clone(),
             SimId::Player1,
         );
-        let wrapper = Viewport::new(event_loop, self.icon.clone(), Box::new(app));
-        self.focused = Some(wrapper.id());
-        self.viewports.insert(wrapper.id(), wrapper);
+        self.open(event_loop, Box::new(app));
+        if let Some(port) = self.init_debug_port {
+            let mut server = GdbServerWindow::new(SimId::Player1, self.client.clone());
+            server.start(port);
+            self.open(event_loop, Box::new(server));
+        }
     }
 
     fn window_event(
diff --git a/src/main.rs b/src/main.rs
index e9abf8e..0d97e7d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -22,7 +22,11 @@ mod window;
 
 #[derive(Parser)]
 struct Args {
+    /// The path to a virtual boy ROM to run.
     rom: Option<PathBuf>,
+    /// Start a GDB/LLDB debug server on this port.
+    #[arg(short, long)]
+    debug_port: Option<u16>,
 }
 
 fn set_panic_handler() {
@@ -101,6 +105,6 @@ fn main() -> Result<()> {
     let event_loop = EventLoop::with_user_event().build().unwrap();
     event_loop.set_control_flow(ControlFlow::Poll);
     let proxy = event_loop.create_proxy();
-    event_loop.run_app(&mut Application::new(client, proxy))?;
+    event_loop.run_app(&mut Application::new(client, proxy, args.debug_port))?;
     Ok(())
 }
diff --git a/src/window/gdb.rs b/src/window/gdb.rs
index c96c169..9d6fa0f 100644
--- a/src/window/gdb.rs
+++ b/src/window/gdb.rs
@@ -21,6 +21,12 @@ impl GdbServerWindow {
             server: GdbServer::new(sim_id, client),
         }
     }
+
+    pub fn start(&mut self, port: u16) {
+        self.server.stop();
+        self.port_str = port.to_string();
+        self.server.start(port);
+    }
 }
 
 impl AppWindow for GdbServerWindow {