diff --git a/hostsoftware/src/main.rs b/hostsoftware/src/main.rs
index dddbbc5..039ee31 100644
--- a/hostsoftware/src/main.rs
+++ b/hostsoftware/src/main.rs
@@ -102,7 +102,10 @@ impl eframe::App for CheapsdoControl {
                     });
 
                 if ui
-                    .add_enabled(!self.serial_connected, egui::Button::new("Open"))
+                    .add_enabled(
+                        !self.serial_connected && !self.serial_device.is_empty(),
+                        egui::Button::new("Open"),
+                    )
                     .clicked()
                 {
                     let serial_device = self.serial_device.clone();