diff --git a/crates/ui-egui/src/app.rs b/crates/ui-egui/src/app.rs
index 8cc53258e..fb5e7e3dd 100644
--- a/crates/ui-egui/src/app.rs
+++ b/crates/ui-egui/src/app.rs
@@ -72,6 +72,7 @@ impl SlideApp {
             synthetic_injected_time: None,
             ribbon_scroll: HashMap::new(),
             show_instance: 0,
+            #[cfg(not(target_arch = "wasm32"))]
             opening_generation: 0,
             canvas_rect: None,
             eyedropper: None,
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index b92d088ab..48253bb01 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -276,7 +276,8 @@ pub struct SlideApp {
     ribbon_scroll: HashMap<String, u32>,
     /// Monotonic identity for a new slide show instance (`start_show`).
     show_instance: u64,
-    /// Monotonic identity for a new background-open attempt.
+    /// Monotonic identity for a new background-open attempt (the web build has no threads).
+    #[cfg(not(target_arch = "wasm32"))]
     opening_generation: u64,
     /// Canvas screen rect and points-per-slide-point scale (for control & tests).
     pub canvas_rect: Option<egui::Rect>,