diff --git a/src/help_window.cpp b/src/help_window.cpp
index a9065f3..edb27ef 100644
--- a/src/help_window.cpp
+++ b/src/help_window.cpp
@@ -13,13 +13,14 @@
 namespace udpscope {
 namespace {
 
-/// Nulled by the `close-request` handler so a second open cannot present a dead widget.
+/// Nulled by each window's own close handler, so a second open cannot present a dead widget.
 /// One pointer per window, file-scope because there is one application.
-GtkWidget* g_about = nullptr;
+///
+/// The help window is a `GtkWindow`. The other two are `AdwDialog`s, which are **not**
+/// `GtkWindow`s: they have no `::close-request`, so they clear on `::closed` and close with
+/// `adw_dialog_close()`.
 GtkWidget* g_help = nullptr;
-
-/// The shortcut overview is an `AdwDialog`, not a window, so it has its own pointer and
-/// its own clearing signal (`::closed` rather than `::close-request`).
+AdwDialog* g_about = nullptr;
 AdwDialog* g_shortcuts = nullptr;
 
 gboolean on_window_close(GtkWindow* window, gpointer slot) {
@@ -28,10 +29,11 @@ gboolean on_window_close(GtkWindow* window, gpointer slot) {
   return FALSE;  // let the default handler destroy it
 }
 
-void on_shortcuts_closed(AdwDialog* dialog, gpointer user) {
+/// Shared by both `AdwDialog`s: the pointer to clear is the `user_data`, so there is one
+/// handler rather than one per dialog.
+void on_dialog_closed(AdwDialog* dialog, gpointer slot) {
   (void)dialog;
-  (void)user;
-  g_shortcuts = nullptr;
+  *static_cast<AdwDialog**>(slot) = nullptr;
 }
 
 struct HelpPage {
@@ -98,31 +100,41 @@ void on_help_row_selected(GtkListBox*, GtkListBoxRow* row, gpointer body_label)
 
 void show_about(GtkWindow* parent, const std::string& session_path) {
   if (g_about != nullptr) {
-    gtk_window_present(GTK_WINDOW(g_about));
+    adw_dialog_present(g_about, GTK_WIDGET(parent));
     return;
   }
 
-  // GtkAboutDialog is not deprecated in GTK 4 (unlike GtkShortcutsWindow), so the
-  // stock dialog is used here and the overview is hand-rolled.
-  GtkWidget* dialog = gtk_about_dialog_new();
+  // `AdwAboutDialog` rather than `GtkAboutDialog`: it shows the application icon as the page's
+  // own header, which is the whole reason the app has one, and `adw_about_window_new()` is
+  // deprecated in favour of it. It is an `AdwDialog`, so it is modal on what it is presented
+  // on and needs no transient-for or modal call of its own.
+  AdwDialog* dialog = adw_about_dialog_new();
   g_about = dialog;
-  GtkAboutDialog* about = GTK_ABOUT_DIALOG(dialog);
-  gtk_about_dialog_set_program_name(about, "udpscope");
-  gtk_about_dialog_set_version(about, build_info::kVersion);
-  gtk_about_dialog_set_comments(about, "An oscilloscope for UDPStreamer sources.");
-  gtk_about_dialog_set_license_type(about, GTK_LICENSE_MIT_X11);
+  AdwAboutDialog* about = ADW_ABOUT_DIALOG(dialog);
+  adw_about_dialog_set_application_name(about, "udpscope");
+  adw_about_dialog_set_application_icon(about, "org.udpscope.app");
+  adw_about_dialog_set_developer_name(about, "Martino Ferrari");
+  adw_about_dialog_set_version(about, build_info::kVersion);
+  adw_about_dialog_set_comments(about, "An oscilloscope for UDPStreamer sources.");
+  adw_about_dialog_set_license_type(about, GTK_LICENSE_MIT_X11);
+  adw_about_dialog_set_website(about, "https://git.ferrarinas.it/martino/udpscope");
 
-  char details[1024];
-  std::snprintf(details, sizeof(details),
-                "Commit: %s\nBuilt: %s\nSettings: %s\nSession file: %s",
-                build_info::kCommit, build_info::kTimestamp, config_dir().c_str(),
-                session_path.c_str());
-  gtk_about_dialog_set_system_information(about, details);
+  // `debug_info` rather than `system_information`: it renders as a Troubleshooting page with a
+  // copy button, where the old field was inert text a user had to retype. A `std::string`
+  // rather than a fixed buffer, because a long settings path used to truncate it silently.
+  const std::string debug = "Commit: " + std::string(build_info::kCommit) +
+                            "\nBuilt: " + build_info::kTimestamp +
+                            "\nSettings: " + config_dir() +
+                            "\nSession file: " + session_path;
+  adw_about_dialog_set_debug_info(about, debug.c_str());
 
-  gtk_window_set_transient_for(GTK_WINDOW(dialog), parent);
-  gtk_window_set_modal(GTK_WINDOW(dialog), TRUE);
-  g_signal_connect(dialog, "close-request", G_CALLBACK(on_window_close), &g_about);
-  gtk_window_present(GTK_WINDOW(dialog));
+  g_signal_connect(dialog, "closed", G_CALLBACK(on_dialog_closed), &g_about);
+  adw_dialog_present(dialog, GTK_WIDGET(parent));
+}
+
+const char* about_icon_name() {
+  if (g_about == nullptr) return "";
+  return adw_about_dialog_get_application_icon(ADW_ABOUT_DIALOG(g_about));
 }
 
 HelpReport help_self_check() {
@@ -278,13 +290,13 @@ void show_shortcuts(GtkWindow* parent) {
                     gestures[i].description);
   }
 
-  g_signal_connect(dialog, "closed", G_CALLBACK(on_shortcuts_closed), nullptr);
+  g_signal_connect(dialog, "closed", G_CALLBACK(on_dialog_closed), &g_shortcuts);
   adw_dialog_present(dialog, GTK_WIDGET(parent));
 }
 
 void close_help_windows() {
   if (g_help != nullptr) gtk_window_close(GTK_WINDOW(g_help));
-  if (g_about != nullptr) gtk_window_close(GTK_WINDOW(g_about));
+  if (g_about != nullptr) adw_dialog_close(g_about);
   if (g_shortcuts != nullptr) adw_dialog_close(g_shortcuts);
 }
 
diff --git a/src/help_window.hpp b/src/help_window.hpp
index 8571e29..3eeb064 100644
--- a/src/help_window.hpp
+++ b/src/help_window.hpp
@@ -8,10 +8,16 @@
 
 namespace udpscope {
 
-/// The About dialog: version, commit, build timestamp and where the session files live.
-/// Modal on `parent`. `session_path` is this run's own session file.
+/// The About dialog: the app icon, version, commit, build timestamp and where the session
+/// files live. An `AdwAboutDialog`, so it is modal on `parent` by being presented on it, and
+/// it is an `AdwDialog` rather than a `GtkWindow`. `session_path` is this run's own session
+/// file; it goes on the Troubleshooting page, which has a copy button.
 void show_about(GtkWindow* parent, const std::string& session_path);
 
+/// The icon name the open About dialog carries, or "" when it is not open. The probe reads it
+/// so the dialog is asserted to *show* the app icon rather than merely to open.
+const char* about_icon_name();
+
 /// The paged help window. Modal on nothing — it is a reference, so it stays usable while
 /// the scope runs. Already open: presented.
 void show_help(GtkWindow* parent);
@@ -33,10 +39,11 @@ HelpReport help_self_check();
 /// deprecated as of GTK 4.18 and this project builds warning-free.
 void show_shortcuts(GtkWindow* parent);
 
-/// Closes whichever of the three windows are open. The About dialog and the help window are
-/// GtkWindows and close with gtk_window_close(), so their close-request handlers run; the
-/// shortcut overview is an AdwDialog and closes with adw_dialog_close(), which emits ::closed.
-/// Either way the file-scope pointer is nulled by the handler. Used by the probe.
+/// Closes whichever of the three windows are open. One of them is a GtkWindow -- the help
+/// window, closed with gtk_window_close(), which emits close-request so its handler runs. The
+/// other two are AdwDialogs, which are not GtkWindows: they close with adw_dialog_close(),
+/// which emits ::closed. Either way the file-scope pointer is nulled by the handler, which is
+/// what prevents a second open presenting a dead widget. Used by the probe.
 void close_help_windows();
 
 }  // namespace udpscope
diff --git a/src/ui.cpp b/src/ui.cpp
index 5b3dbfe..33877a8 100644
--- a/src/ui.cpp
+++ b/src/ui.cpp
@@ -7568,6 +7568,9 @@ gboolean help_probe(gpointer user) {
   show_help(GTK_WINDOW(a->window));
   show_about(GTK_WINDOW(a->window), session);
   show_shortcuts(GTK_WINDOW(a->window));
+  // Read while it is open: the icon is the point of the dialog carrying one, and
+  // `close_help_windows()` is right below.
+  const std::string about_icon = about_icon_name();
   close_help_windows();
 
   int accel_count = 0;
@@ -7576,10 +7579,11 @@ gboolean help_probe(gpointer user) {
   (void)plot_gestures(&gesture_count);
   std::fprintf(stderr,
                "[help] pages=%d parsed=%d shortest='%s' %zu B; shortcuts: app=%d plot=%d; "
-               "about version=%s commit=%s built=%s settings=%s; closed ok\n",
+               "about version=%s commit=%s built=%s settings=%s icon=%s; closed ok\n",
                report.pages, report.parsed, report.shortest_title.c_str(),
                report.shortest_bytes, accel_count, gesture_count, build_info::kVersion,
-               build_info::kCommit, build_info::kTimestamp, config_dir().c_str());
+               build_info::kCommit, build_info::kTimestamp, config_dir().c_str(),
+               about_icon.c_str());
   std::fflush(stderr);
   return G_SOURCE_REMOVE;
 }