diff --git a/src/ui/main_window.rs b/src/ui/main_window.rs
index 33e078a..47ba0d5 100644
--- a/src/ui/main_window.rs
+++ b/src/ui/main_window.rs
@@ -56,6 +56,19 @@ impl MainWindow {
                         return Task::none();
                     }
                     iced::window::Event::CloseRequested => {
+                        // Suppress the close while an operation is in progress
+                        // so OpenOCD (or the FUS upgrade) isn't interrupted
+                        // mid-action. The opacity overlay already signals the
+                        // busy state visually; the user can force-quit / end
+                        // task the app if they really need out, but a misclick
+                        // on the X shouldn't brick the device.
+                        if self.tab_daplink.is_busy() || self.tab_ws.is_busy() {
+                            eprintln!(
+                                "Close request ignored: an operation is in progress."
+                            );
+                            return Task::none();
+                        }
+
                         match dirs::get_settings_dir() {
                             Ok(settings_dir) => {
                                 let fields_file = settings_dir.join(SETTINGS_FILE);
diff --git a/src/ui/tab_daplink.rs b/src/ui/tab_daplink.rs
index c630117..8b703bf 100644
--- a/src/ui/tab_daplink.rs
+++ b/src/ui/tab_daplink.rs
@@ -38,6 +38,14 @@ pub struct TabDaplink {
 }
 
 impl TabDaplink {
+    /// True while an operation that should not be interrupted is running:
+    /// a flash sequence, or a (modal) file-browse. Used by `MainWindow` to
+    /// suppress window-close requests so the OpenOCD child isn't killed
+    /// mid-write.
+    pub fn is_busy(&self) -> bool {
+        self.is_readonly
+    }
+
     pub fn update(&mut self, message: TabDaplinkMessage) -> Task<Message> {
         match message {
             TabDaplinkMessage::LogMessage(log) => self.log_widget.push(log),
diff --git a/src/ui/tab_wireless_stack.rs b/src/ui/tab_wireless_stack.rs
index 42bccf6..62fd210 100644
--- a/src/ui/tab_wireless_stack.rs
+++ b/src/ui/tab_wireless_stack.rs
@@ -103,6 +103,13 @@ const ALL_STACK: [WirelessStackFile; 21] = [
 ];
 
 impl TabWirelessStack {
+    /// True while an operation that should not be interrupted is running.
+    /// Used by `MainWindow` to suppress window-close requests so neither
+    /// the OpenOCD child nor an in-flight FUS upgrade gets cut mid-action.
+    pub fn is_busy(&self) -> bool {
+        self.is_readonly
+    }
+
     pub fn view(&self) -> Element<Message> {
         let grid_fields = grid!(
             grid_row!(