diff --git a/render-wasm/src/render.rs b/render-wasm/src/render.rs
index 44b0c7e674..5ae705a7bd 100644
--- a/render-wasm/src/render.rs
+++ b/render-wasm/src/render.rs
@@ -422,6 +422,21 @@ impl RenderState {
         })
     }
 
+    /// Device scale when workspace zoom is 100% (`viewbox.zoom == 1`): `1.0 * dpr`.
+    fn base_zoom_placeholder_scale_bits(&self) -> u32 {
+        (1.0_f32 * self.options.dpr()).to_bits()
+    }
+
+    /// Scale bits used to look up tile textures in the cache.
+    /// In `fast_mode`, always use the 100% zoom cache; otherwise use current scale.
+    fn tile_texture_cache_lookup_scale_bits(&self) -> u32 {
+        if self.options.is_fast_mode() {
+            self.base_zoom_placeholder_scale_bits()
+        } else {
+            self.get_scale().to_bits()
+        }
+    }
+
     fn rect_union(a: Rect, b: Rect) -> Rect {
         Rect::from_ltrb(
             a.left().min(b.left()),
@@ -1489,6 +1504,9 @@ impl RenderState {
                                 target_world_rect,
                                 current_scale,
                                 current_scale_bits,
+                                self.options
+                                    .is_fast_mode()
+                                    .then_some(self.base_zoom_placeholder_scale_bits()),
                                 true,
                             );
                         }
@@ -1576,9 +1594,14 @@ impl RenderState {
 
         let _tile_start = performance::begin_timed_log!("tile_cache_update");
         performance::begin_measure!("tile_cache");
-        let scale_bits = scale.to_bits();
-        self.pending_tiles
-            .update(&self.tile_viewbox, &self.surfaces, scale_bits);
+        let lookup_bits = self.tile_texture_cache_lookup_scale_bits();
+        self.pending_tiles.update(
+            &self.tile_viewbox,
+            &self.surfaces,
+            scale,
+            self.options.is_fast_mode(),
+            lookup_bits,
+        );
         performance::end_measure!("tile_cache");
         performance::end_timed_log!("tile_cache_update", _tile_start);
 
@@ -2612,16 +2635,14 @@ impl RenderState {
         while !should_stop {
             if let Some(current_tile) = self.current_tile {
                 let scale = self.get_scale();
-                let scale_bits = scale.to_bits();
-                if self
-                    .surfaces
-                    .has_cached_tile_surface(current_tile, scale_bits)
-                {
+                let lookup_bits = self.tile_texture_cache_lookup_scale_bits();
+                let fast_mode = self.options.is_fast_mode();
+                if !fast_mode && self.surfaces.has_cached_tile_surface(current_tile, lookup_bits) {
                     performance::begin_measure!("render_shape_tree::cached");
                     let tile_rect = self.get_current_tile_bounds()?;
                     self.surfaces.draw_cached_tile_surface(
                         current_tile,
-                        scale_bits,
+                        lookup_bits,
                         tile_rect,
                         self.background_color,
                     );
@@ -2646,7 +2667,8 @@ impl RenderState {
                         self.background_color,
                         target_world_rect,
                         scale,
-                        scale_bits,
+                        lookup_bits,
+                        fast_mode.then_some(self.base_zoom_placeholder_scale_bits()),
                         true,
                     );
                     performance::begin_measure!("render_shape_tree::uncached");
diff --git a/render-wasm/src/render/surfaces.rs b/render-wasm/src/render/surfaces.rs
index d7dbc4c0cc..dd0067edff 100644
--- a/render-wasm/src/render/surfaces.rs
+++ b/render-wasm/src/render/surfaces.rs
@@ -566,6 +566,24 @@ impl Surfaces {
         self.tiles.has(tile, scale_bits)
     }
 
+    pub fn world_rect_has_any_tile_at_scale_bits(&self, world_rect: Rect, scale_bits: u32) -> bool {
+        let scale = f32::from_bits(scale_bits);
+        if !scale.is_finite() || scale <= 0.0 {
+            return false;
+        }
+        let tile_size_world = super::tiles::get_tile_size(scale);
+        let super::tiles::TileRect(sx, sy, ex, ey) =
+            super::tiles::get_tiles_for_rect(world_rect, tile_size_world);
+        for x in sx..=ex {
+            for y in sy..=ey {
+                if self.tiles.has_stale(Tile::from(x, y), scale_bits) {
+                    return true;
+                }
+            }
+        }
+        false
+    }
+
     pub fn cached_scale_bits(&self) -> Vec<u32> {
         self.tiles.scale_bits().collect()
     }
@@ -670,6 +688,7 @@ impl Surfaces {
     }
 
     /// Draw a placeholder for a missing tile using cached tiles from other zoom levels.
+    /// If `forced_src_scale_bits` is set, only that scale is used as the source (used by fast_mode).
     pub fn draw_tile_fallback_cross_zoom(
         &mut self,
         tile_viewbox: &TileViewbox,
@@ -678,12 +697,15 @@ impl Surfaces {
         target_world_rect: Rect,
         target_scale: f32,
         target_scale_bits: u32,
+        forced_src_scale_bits: Option<u32>,
         debug_trace: bool,
     ) -> usize {
-        let Some(candidate_scale_bits) = self
-            .tiles
-            .best_fallback_scale_bits(target_scale, target_scale_bits)
-        else {
+        let Some(candidate_scale_bits) = (if let Some(bits) = forced_src_scale_bits {
+            Some(bits)
+        } else {
+            self.tiles
+                .best_fallback_scale_bits(target_scale, target_scale_bits)
+        }) else {
             if debug_trace {
             }
             return 0;
@@ -706,7 +728,12 @@ impl Surfaces {
         for x in sx..=ex {
             for y in sy..=ey {
                 let src_tile = Tile::from(x, y);
-                let Some(src_image) = self.tiles.get(src_tile, candidate_scale_bits) else {
+                let src_image_opt = if forced_src_scale_bits.is_some() {
+                    self.tiles.get_stale(src_tile, candidate_scale_bits)
+                } else {
+                    self.tiles.get(src_tile, candidate_scale_bits)
+                };
+                let Some(src_image) = src_image_opt else {
                     continue;
                 };
 
@@ -833,6 +860,12 @@ impl TileTextureCache {
         self.grid.contains_key(&key) && !self.removed.contains(&key)
     }
 
+    /// Like `has` but ignores the `removed` tombstone (stale placeholder).
+    pub fn has_stale(&self, tile: Tile, scale_bits: u32) -> bool {
+        let key = TileCacheKey { tile, scale_bits };
+        self.grid.contains_key(&key)
+    }
+
     fn gc(&mut self) {
         println!("gc");
         // Make a real remove
@@ -896,6 +929,12 @@ impl TileTextureCache {
         self.grid.get(&key)
     }
 
+    /// Like `get` but returns the image even if it is marked as `removed`.
+    pub fn get_stale(&self, tile: Tile, scale_bits: u32) -> Option<&skia::Image> {
+        let key = TileCacheKey { tile, scale_bits };
+        self.grid.get(&key)
+    }
+
     pub fn remove(&mut self, tile: Tile, scale_bits: u32) {
         self.removed.insert(TileCacheKey { tile, scale_bits });
     }
diff --git a/render-wasm/src/tiles.rs b/render-wasm/src/tiles.rs
index 318b91b04c..8bde91668c 100644
--- a/render-wasm/src/tiles.rs
+++ b/render-wasm/src/tiles.rs
@@ -261,7 +261,14 @@ impl PendingTiles {
         result
     }
 
-    pub fn update(&mut self, tile_viewbox: &TileViewbox, surfaces: &Surfaces, scale_bits: u32) {
+    pub fn update(
+        &mut self,
+        tile_viewbox: &TileViewbox,
+        surfaces: &Surfaces,
+        current_scale: f32,
+        fast_mode: bool,
+        lookup_scale_bits: u32,
+    ) {
         self.list.clear();
 
         // Generate spiral for the interest area (viewport + margin)
@@ -279,7 +286,14 @@ impl PendingTiles {
 
         for tile in spiral {
             let is_visible = tile_viewbox.visible_rect.contains(&tile);
-            let is_cached = surfaces.has_cached_tile_surface(tile, scale_bits);
+            let is_cached = if fast_mode {
+                // fast_mode reads only 100% zoom cache; tile indices differ across scales,
+                // so decide cacheability by world rect coverage at the lookup scale.
+                let world_rect = super::tiles::get_tile_rect(tile, current_scale);
+                surfaces.world_rect_has_any_tile_at_scale_bits(world_rect, lookup_scale_bits)
+            } else {
+                surfaces.has_cached_tile_surface(tile, lookup_scale_bits)
+            };
 
             match (is_visible, is_cached) {
                 (true, true) => visible_cached.push(tile),