diff --git a/crates/render/src/lib.rs b/crates/render/src/lib.rs
index f88d492a..7c78c411 100644
--- a/crates/render/src/lib.rs
+++ b/crates/render/src/lib.rs
@@ -1056,6 +1056,17 @@ impl Renderer {
             ctx.push_layer(None, None, None, None, None);
             let _ = r;
         }
+        // Shape-space units per point for the 3-D sizes, measured without the camera's turn (which
+        // `shape_at` puts in `m`): its foreshortening is not a child-coordinate scale.
+        let pt = {
+            let turn = effects
+                .as_ref()
+                .and_then(|e| e.raw3d.as_deref())
+                .and_then(camera::from_raw)
+                .and_then(|c| camera::affine(&c, w, h))
+                .filter(|t| t.determinant().abs() > 1e-9);
+            self.per_point(turn.map_or(m, |t| m * t.inverse()), depth)
+        };
         // A 3-D extrusion under a turned camera: the sides, swept behind the face.
         if let Some(raw) = effects.as_ref().and_then(|e| e.raw3d.as_deref())
             && let Some(ex) = extrude::from_raw(raw)
@@ -1069,7 +1080,7 @@ impl Renderer {
             };
             let pre = m * turn.inverse();
             let lit = light::Lighting::from_raw(raw);
-            let d = ex.depth * self.per_point(m, depth);
+            let d = ex.depth * pt;
             extrude::draw(ctx, &outline, w, h, &cam, d, pre, turn, extrude::side_color(rctx, &ex, face), &lit);
         }
         // A 3-D contour: a band around the outline, behind the face (and in front of any sides).
@@ -1081,7 +1092,7 @@ impl Renderer {
                 _ => None,
             };
             let col = c.color.as_ref().map(|k| rctx.color(k, face)).or(face).unwrap_or(Rgba::rgb(0xff, 0xff, 0xff));
-            extrude::draw_contour(ctx, &outline, m, c.width * self.per_point(m, depth), col, &light::Lighting::from_raw(raw));
+            extrude::draw_contour(ctx, &outline, m, c.width * pt, col, &light::Lighting::from_raw(raw));
         }
         // Fill.
         match &s.kind {
@@ -1176,8 +1187,7 @@ impl Renderer {
         };
         // A 3-D bevel: the face and a band inside the outline lit as surfaces.
         if let Some(bv) = effects.as_ref().and_then(|e| e.raw3d.as_deref()).and_then(bevel::from_raw) {
-            let k = self.per_point(m, depth);
-            let bv = bevel::Bevel { w: bv.w * k, h: bv.h * k, ..bv };
+            let bv = bevel::Bevel { w: bv.w * pt, h: bv.h * pt, ..bv };
             let solid = match &fill {
                 Some(Fill::Solid { color: c }) => Some(rctx.color(c, fill_ph)),
                 _ => None,
diff --git a/crates/render/src/tests.rs b/crates/render/src/tests.rs
index d7122f05..348b89c3 100644
--- a/crates/render/src/tests.rs
+++ b/crates/render/src/tests.rs
@@ -2310,6 +2310,36 @@ fn group_child_scale_does_not_scale_3d_depth_contours_or_bevels() {
     assert!(d * 20 < drawn, "{d} differing values against {drawn} inked pixels");
 }
 
+#[test]
+fn a_turned_camera_in_a_one_to_one_group_draws_its_3d_sizes_as_outside_one() {
+    // The camera's turn is part of the shape's transform; its foreshortening is not a group scale,
+    // so a 1:1 group must not change extrusion depths, contours or bevels under a turned camera.
+    let mut deck = extruded_deck();
+    let bevelled = Shape {
+        id: ShapeId(705),
+        xfrm: Some(Xfrm::new(40.0, 340.0, 170.0, 130.0)),
+        geom: Geom::preset("rect"),
+        style: Some(ShapeStyle::accent(deckcraft_color::SchemeSlot::Accent1)),
+        effects: Some(deckcraft_model::Effects {
+            raw3d: Some(r#"<a:scene3d><a:camera prst="isometricOffAxis1Right"/><a:lightRig rig="threePt" dir="t"/></a:scene3d><a:sp3d extrusionH="254000" contourW="38100"><a:bevelT w="254000" h="254000"/></a:sp3d>"#.into()),
+            ..Default::default()
+        }),
+        ..Default::default()
+    };
+    std::sync::Arc::make_mut(&mut deck.slides[0]).shapes.push(bevelled);
+    let opts = RenderOpts { scale: 1.0, ..Default::default() };
+    let alone = render_slide(&deck, 0, &opts);
+    let group = Shape {
+        id: ShapeId(10),
+        xfrm: Some(Xfrm::new(0.0, 0.0, 960.0, 540.0)),
+        kind: ShapeKind::Group { children: deck.slides[0].shapes.clone(), child: Xfrm::new(0.0, 0.0, 960.0, 540.0) },
+        ..Default::default()
+    };
+    let grouped = render_slide(&deck_with(vec![group]), 0, &opts);
+    let d = differing(&alone, &grouped);
+    assert!(d < 200, "{d} values differ between the shapes alone and in a 1:1 group");
+}
+
 #[test]
 fn table_rows_below_the_slide_are_not_laid_out_and_the_slide_looks_the_same() {
     // A fuzzed deck's 200 x 200 table of long text took 70 s to draw, most of it off the slide.