diff --git a/crates/ui-egui/src/app.rs b/crates/ui-egui/src/app.rs
index 17d57fd01c..e31411c4b2 100644
--- a/crates/ui-egui/src/app.rs
+++ b/crates/ui-egui/src/app.rs
@@ -354,6 +354,7 @@ impl WordApp {
         if !native {
             self.window_input(ctx);
         }
+        self.sync_viewport_input(ctx);
         self.send_control_input(ctx);
         // Screenshot deadlines, geometry and completions belong to `logic`; issuing the one
         // callback command belongs to `ui` (`flush_shot_and_synthetic`). A queued/settling capture
diff --git a/crates/ui-egui/src/windows.rs b/crates/ui-egui/src/windows.rs
index 9b83c996c3..36b38008a4 100644
--- a/crates/ui-egui/src/windows.rs
+++ b/crates/ui-egui/src/windows.rs
@@ -766,10 +766,10 @@ impl WordApp {
         }
     }
 
-    /// The control channel's next input, for the active window when it has a viewport of its own:
-    /// handed to [`ViewportInput`], which gives it to that viewport's next pass.
-    pub(crate) fn send_control_input(&mut self, ctx: &egui::Context) {
-        if self.synthetic.is_empty() || self.control_input_is_roots(ctx) {
+    /// Ensures [`ViewportInput`] is registered and keeps its touchpad scroll speed in sync with
+    /// user settings for secondary viewports (#6146).
+    pub(crate) fn sync_viewport_input(&mut self, ctx: &egui::Context) {
+        if !self.windows.native {
             return;
         }
         if !self.windows.input_plugin {
@@ -780,6 +780,15 @@ impl WordApp {
         ctx.with_plugin(|p: &mut ViewportInput| {
             p.touchpad_speed = speed;
         });
+    }
+
+    /// The control channel's next input, for the active window when it has a viewport of its own:
+    /// handed to [`ViewportInput`], which gives it to that viewport's next pass.
+    pub(crate) fn send_control_input(&mut self, ctx: &egui::Context) {
+        if self.synthetic.is_empty() || self.control_input_is_roots(ctx) {
+            return;
+        }
+        self.sync_viewport_input(ctx);
         self.settle_windows();
         let target = self.active_viewport();
         // Input queued for a window that has closed since (or moved into the root viewport)
diff --git a/crates/ui-egui/src/windows/tests.rs b/crates/ui-egui/src/windows/tests.rs
index 444d353606..11436fa42f 100644
--- a/crates/ui-egui/src/windows/tests.rs
+++ b/crates/ui-egui/src/windows/tests.rs
@@ -777,3 +777,13 @@ fn newly_opened_window_does_not_exceed_screen_width() {
     std::fs::remove_dir_all(doc1.parent().unwrap()).ok();
     std::fs::remove_dir_all(doc2.parent().unwrap()).ok();
 }
+
+#[test]
+fn secondary_viewport_syncs_touchpad_scroll_speed_without_control_input() {
+    let ctx = backend();
+    let mut a = WordApp::new(Session::new(wordcraft_doc::Document::new()), Services::default());
+    a.ui.touchpad_scroll_speed = crate::scroll::ScrollSpeed::Fast;
+    frame(&ctx, &mut a);
+    let speed = ctx.with_plugin(|p: &mut super::ViewportInput| p.touchpad_speed);
+    assert_eq!(speed, Some(crate::scroll::ScrollSpeed::Fast));
+}