diff --git a/crates/render/src/lib.rs b/crates/render/src/lib.rs
index c9fe024..fe7ca39 100644
--- a/crates/render/src/lib.rs
+++ b/crates/render/src/lib.rs
@@ -1105,10 +1105,7 @@ impl Renderer {
         if let Some(sh) = &e.outer_shadow {
             let c = rctx.color(&sh.color, ph);
             let d = Vec2::new(sh.dir.to_radians().cos(), sh.dir.to_radians().sin()) * sh.dist;
-            let c0 = Point::new(w / 2.0, h / 2.0);
-            let local = Affine::translate(c0.to_vec2())
-                * Affine::new([sh.sx, sh.ky.to_radians().tan(), sh.kx.to_radians().tan(), sh.sy, 0.0, 0.0])
-                * Affine::translate(-c0.to_vec2());
+            let local = shadow_local(sh, w, h);
             // Shadow offset is in slide space (doesn't rotate with the shape unless asked).
             let sm = if sh.rotate_with_shape { m * Affine::translate(d) * local } else { pre_translate(m, d * k) * local };
             ctx.set_transform(Affine::IDENTITY);
@@ -1169,6 +1166,32 @@ impl Renderer {
     }
 }
 
+/// A shadow's own scale and skew (`sx`, `sy`, `kx`, `ky`) in the shape's space, about the point
+/// of the shape's box its alignment names (`algn`: `b` is the middle of the bottom edge, `tl` the
+/// top-left corner…), as PowerPoint applies them: skewed, then scaled. A perspective shadow
+/// (`algn="b"`, `sy` 23%, `kx` -20°) so lies flat along the shape's bottom edge, not around its
+/// middle.
+fn shadow_local(sh: &deckcraft_model::style::Shadow, w: f64, h: f64) -> Affine {
+    let (ax, ay) = match sh.align.as_str() {
+        "tl" => (0.0, 0.0),
+        "t" => (0.5, 0.0),
+        "tr" => (1.0, 0.0),
+        "l" => (0.0, 0.5),
+        "r" => (1.0, 0.5),
+        "bl" => (0.0, 1.0),
+        "b" => (0.5, 1.0),
+        "br" => (1.0, 1.0),
+        _ => (0.5, 0.5),
+    };
+    let a = Vec2::new(w * ax, h * ay);
+    let (tx, ty) = (sh.kx.to_radians().tan(), sh.ky.to_radians().tan());
+    let k = Affine::new([sh.sx, sh.sy * ty, sh.sx * tx, sh.sy, 0.0, 0.0]);
+    if !k.is_finite() {
+        return Affine::IDENTITY;
+    }
+    Affine::translate(a) * k * Affine::translate(-a)
+}
+
 fn pre_translate(m: Affine, d: Vec2) -> Affine {
     Affine::translate(d) * m
 }
diff --git a/crates/render/src/tests_wild.rs b/crates/render/src/tests_wild.rs
index 5f87c7a..c1ec2ef 100644
--- a/crates/render/src/tests_wild.rs
+++ b/crates/render/src/tests_wild.rs
@@ -189,3 +189,39 @@ fn a_radial_gradient_off_centre_ends_on_the_circle_around_the_box() {
     assert!(img.pixel(300, 200)[0] > 240 && img.pixel(101, 101)[0] < 60);
     assert!((img.pixel(110, 200)[0] as i32 - img.pixel(490, 200)[0] as i32).abs() <= 2);
 }
+
+fn shadow(sx: f64, sy: f64, kx: f64, align: &str) -> deckcraft_model::style::Shadow {
+    deckcraft_model::style::Shadow {
+        color: ColorRef::rgb(Rgba::BLACK),
+        blur: 0.0,
+        dist: 0.0,
+        dir: 0.0,
+        inner: false,
+        sx,
+        sy,
+        kx,
+        ky: 0.0,
+        align: align.into(),
+        rotate_with_shape: false,
+    }
+}
+
+fn with_effects(fill: Option<Fill>, line: Option<Line>, effects: deckcraft_model::Effects) -> Shape {
+    Shape { id: ShapeId(14), xfrm: Some(Xfrm::new(100.0, 100.0, 100.0, 100.0)), fill, line, effects: Some(effects), ..Default::default() }
+}
+
+#[test]
+fn a_perspective_shadow_lies_along_the_edge_its_alignment_names() {
+    // Half height, skewed 45° so its top leans right, anchored at the bottom middle: the shadow's
+    // bottom edge is the shape's (y = 200) and its top (y = 150) is 50 pt to the right.
+    let fx = deckcraft_model::Effects { outer_shadow: Some(shadow(1.0, 0.5, -45.0, "b")), ..Default::default() };
+    let img = render(vec![with_effects(solid(RED), no_line(), fx)]);
+    assert!(close(img.pixel(210, 175), Rgba::BLACK, 30), "{:?}", img.pixel(210, 175));
+    assert!(close(img.pixel(240, 155), Rgba::BLACK, 30), "{:?}", img.pixel(240, 155));
+    assert!(close(img.pixel(240, 180), WHITE, 10), "{:?}", img.pixel(240, 180));
+    assert!(close(img.pixel(205, 140), WHITE, 10), "nothing above the half height {:?}", img.pixel(205, 140));
+    // Anchored bottom-right and half as big again: it grows up and to the left only.
+    let fx = deckcraft_model::Effects { outer_shadow: Some(shadow(1.5, 1.5, 0.0, "br")), ..Default::default() };
+    let img = render(vec![with_effects(solid(RED), no_line(), fx)]);
+    assert!(close(img.pixel(70, 70), Rgba::BLACK, 30) && close(img.pixel(210, 210), WHITE, 10));
+}