diff --git a/crates/expr/src/host.rs b/crates/expr/src/host.rs
index db38ba805..fa2993f97 100644
--- a/crates/expr/src/host.rs
+++ b/crates/expr/src/host.rs
@@ -10,7 +10,7 @@
 use effectcraft_geom::{Mat3, Mat4};
 use effectcraft_keyframe::Value;
 use effectcraft_project::{Comp, ItemId, ItemKind, Layer, LayerId, LayerSource, Node, PropGroup, Property};
-use effectcraft_render::{EvalCtx, source_size};
+use effectcraft_render::EvalCtx;
 use effectcraft_time::Tick;
 
 /// A name-or-index argument (`layer("A")`, `layer(2)`, `effect(1)`).
@@ -382,7 +382,7 @@ impl<'a> Resolver<'a> {
             Req::LayerInfo { comp, layer } => {
                 let c = self.comp(*comp)?;
                 let l = self.layer(*comp, *layer)?;
-                let (mut w, mut h) = source_size(project, l);
+                let (mut w, mut h) = self.ctx_at(*comp, self.ctx.time.seconds())?.source_size(l);
                 if w == 0 || h == 0 {
                     (w, h) = (c.width, c.height);
                 }
@@ -477,7 +477,7 @@ impl<'a> Resolver<'a> {
                         }
                     }
                     _ => {
-                        let (w, h) = source_size(project, l);
+                        let (w, h) = ctx.source_size(l);
                         [0.0, 0.0, w as f64, h as f64]
                     }
                 };
@@ -511,7 +511,12 @@ impl<'a> Resolver<'a> {
             Req::SourceInfo { comp, layer } => {
                 let c = self.comp(*comp)?;
                 let l = self.layer(*comp, *layer)?;
-                let it = project.item(l.source.item()?)?;
+                let ctx = self.ctx_at(*comp, self.ctx.time.seconds())?;
+                let item = match &l.source {
+                    LayerSource::Footage { item } => ctx.media_item(l, *item),
+                    _ => l.source.item()?,
+                };
+                let it = project.item(item)?;
                 let (kind, aspect, frame, duration) = match &it.kind {
                     ItemKind::Comp(nc) => ("comp", nc.pixel_aspect, nc.frame_duration().seconds(), nc.duration.seconds()),
                     ItemKind::Footage(f) => ("footage", f.pixel_aspect, f.frame_rate.frame_duration().seconds(), f.duration.seconds()),
diff --git a/crates/expr/src/tests.rs b/crates/expr/src/tests.rs
index a08fd231d..4e7cea0ee 100644
--- a/crates/expr/src/tests.rs
+++ b/crates/expr/src/tests.rs
@@ -907,6 +907,49 @@ fn source_rect_at_time() {
     assert!((s[0] + 31.0).abs() < 2.0 && (s[1] + 16.0).abs() < 2.0 && (s[2] - 62.0).abs() < 3.0, "{s:?}");
 }
 
+#[test]
+fn source_dimensions_follow_media_replacement() {
+    let mut p = Project::default();
+    let comp = Comp::new(200, 100, FrameRate::FPS_30, Tick::from_seconds_f64(2.0));
+    let cid = p.add_item("Main", Label::Sandstone, None, ItemKind::Comp(comp.clone().into()));
+    let footage = |p: &mut Project, name: &str, width, height| {
+        p.add_item(
+            name,
+            Label::SeaFoam,
+            None,
+            ItemKind::Footage(effectcraft_project::Footage {
+                path: name.into(),
+                kind: effectcraft_project::FootageKind::Still,
+                width,
+                height,
+                has_video: true,
+                ..Default::default()
+            }),
+        )
+    };
+    let original = footage(&mut p, "original.png", 100, 80);
+    let replacement = footage(&mut p, "replacement.png", 30, 40);
+    let mut l = build::layer(&mut p, &comp, "Clip", LayerSource::Footage { item: original }, (100, 80), None);
+    l.props.prop_mut(ROT).unwrap().expr =
+        Some(Expression { text: "thisLayer.width + thisLayer.height + thisLayer.source.width + sourceRectAtTime().width".into(), enabled: true });
+    let lid = l.id;
+    p.comp_mut(cid).unwrap().layers.push(l);
+    let c = p.comp(cid).unwrap();
+    let l = c.layer(lid).unwrap();
+    let media = effectcraft_render::MediaOverride::new(lid, replacement);
+    let ctx = EvalCtx {
+        project: &p,
+        comp_id: cid,
+        comp: c,
+        time: Tick::ZERO,
+        expr: Some(&Expressions),
+        footage: None,
+        property_overrides: &[],
+        media_overrides: &[media],
+    };
+    assert_eq!(ctx.value(l, l.props.prop(ROT).unwrap()), Value::Scalar(130.0));
+}
+
 // ---- colour -----------------------------------------------------------------------------------
 
 #[test]