diff --git a/lxplan_lib_creator.py b/lxplan_lib_creator.py
index abe10ae..0836c54 100644
--- a/lxplan_lib_creator.py
+++ b/lxplan_lib_creator.py
@@ -13,6 +13,7 @@ class XMLExtractorApp:
         self.input_file = None
         self.tree = None
         self.additional_fields = {}
+        self.popup_window = None
         
         # Define which fields to show for each kind
         self.kind_fields_map = {
@@ -147,7 +148,7 @@ class XMLExtractorApp:
         
         # Additional fields button
         additional_btn = tk.Button(self.root, text="Additional Fields", 
-                                   command=self.open_additional_fields,
+                                   command=self.toggle_additional_fields,
                                    font=("Arial", 10),
                                    bg="#2196F3", fg="white",
                                    padx=15, pady=8)
@@ -166,6 +167,15 @@ class XMLExtractorApp:
                                      font=("Arial", 9), fg="blue")
         self.status_label.pack(pady=5)
     
+    def toggle_additional_fields(self):
+        # If popup exists and is open, close it
+        if self.popup_window and self.popup_window.winfo_exists():
+            self.popup_window.destroy()
+            self.popup_window = None
+        else:
+            # Otherwise open it
+            self.open_additional_fields()
+    
     def open_additional_fields(self):
         # Get the selected kind value
         selected_display = self.kind_var.get()
@@ -176,10 +186,14 @@ class XMLExtractorApp:
         
         # Create popup window
         popup = tk.Toplevel(self.root)
+        self.popup_window = popup
         popup.title("Additional Fields")
         popup.geometry("500x600")
         popup.resizable(False, False)
         
+        # Handle window close event
+        popup.protocol("WM_DELETE_WINDOW", lambda: self.close_popup(popup))
+        
         # Title
         title = tk.Label(popup, text=f"Additional Fields - {selected_display}", 
                         font=("Arial", 14, "bold"))
@@ -276,9 +290,13 @@ class XMLExtractorApp:
             elif field_name in self.additional_fields:
                 del self.additional_fields[field_name]
         
-        popup.destroy()
+        self.close_popup(popup)
         self.status_label.config(text="Additional fields saved", fg="green")
     
+    def close_popup(self, popup):
+        popup.destroy()
+        self.popup_window = None
+    
     def browse_file(self):
         filename = filedialog.askopenfilename(
             title="Select LXXPLOT File",