diff --git a/crates/engine/src/cmd/mod.rs b/crates/engine/src/cmd/mod.rs
index 228410de..a3d142eb 100644
--- a/crates/engine/src/cmd/mod.rs
+++ b/crates/engine/src/cmd/mod.rs
@@ -324,6 +324,17 @@ pub(crate) fn checked_id(s: &Session, value: &Value, command: &str) -> Result<No
     Ok(id)
 }
 
+/// `v` as exactly `N` finite numbers (`[x, y]`, `[x, y, width, height]`…): `None` when it isn't an
+/// array of that length or an entry isn't a number, so nothing malformed is left out or padded.
+pub(crate) fn finite_numbers<const N: usize>(v: &Value) -> Option<[f64; N]> {
+    let a = v.as_array().filter(|a| a.len() == N)?;
+    let mut out = [0.0; N];
+    for (o, n) in out.iter_mut().zip(a) {
+        *o = n.as_f64().filter(|n| n.is_finite())?;
+    }
+    Some(out)
+}
+
 pub(crate) fn point_param(p: &Value, key: &str) -> Option<Point> {
     let a = p.get(key)?.as_array()?;
     Some(Point::new(a.first()?.as_f64()?, a.get(1)?.as_f64()?))
diff --git a/crates/engine/src/cmd/place/mod.rs b/crates/engine/src/cmd/place/mod.rs
index 9fee1ce5..b881d52b 100644
--- a/crates/engine/src/cmd/place/mod.rs
+++ b/crates/engine/src/cmd/place/mod.rs
@@ -309,13 +309,22 @@ fn transformed(mut node: Node, m: Affine) -> Node {
 /// `[x, y, width, height]` with a positive size.
 fn rect_param(p: &Value) -> Result<Option<Rect>> {
     let Some(v) = p.get("rect") else { return Ok(None) };
-    let n: Vec<f64> = v.as_array().map(|a| a.iter().filter_map(Value::as_f64).collect()).unwrap_or_default();
-    match n[..] {
-        [x, y, w, h] if w > 0.0 && h > 0.0 => Ok(Some(Rect::new(x, y, x + w, y + h))),
+    // All four or nothing: a malformed entry dropped would shift the others ([0, "bad", 10, 40, 50]).
+    match finite_numbers(v) {
+        Some([x, y, w, h]) if w > 0.0 && h > 0.0 => Ok(Some(Rect::new(x, y, x + w, y + h))),
         _ => Err(bad(PLACE, "rect must be [x, y, width, height] with a positive width and height")),
     }
 }
 
+/// `at`, the `[x, y]` the art is centred on (absent or null: none); anything else fails rather than
+/// placing the art as if no point were given.
+fn at_param(p: &Value) -> Result<Option<Point>> {
+    p.get("at")
+        .filter(|v| !v.is_null())
+        .map(|v| finite_numbers(v).map(|[x, y]| Point::new(x, y)).ok_or_else(|| bad(PLACE, "at must be [x, y]")))
+        .transpose()
+}
+
 /// The transform that puts new art with the natural box `natural` where `old` is: an image's scale
 /// and rotation relative to its 100% size (its resolution's) and its centre are kept (with
 /// `image_xf`); other objects keep their centre.
@@ -342,7 +351,7 @@ fn fit(natural: Rect, r: Rect) -> Affine {
 fn place(s: &mut Session, p: &Value) -> Result<Value> {
     let replace = bool_or(p, "replace", false);
     let template = bool_or(p, "template", false);
-    let at = point_param(p, "at");
+    let at = at_param(p)?;
     let rect = rect_param(p)?;
     if replace && (template || at.is_some() || rect.is_some()) {
         return Err(bad(PLACE, "replace keeps the replaced object's place and transform: drop template, at and rect"));
diff --git a/crates/engine/src/tests_place.rs b/crates/engine/src/tests_place.rs
index aba974e5..0fb2c5d7 100644
--- a/crates/engine/src/tests_place.rs
+++ b/crates/engine/src/tests_place.rs
@@ -57,6 +57,37 @@ fn serialize(s: &mut Session, format: &str) -> Vec<u8> {
     vectorcraft_format::base64_decode(v["dataBase64"].as_str().unwrap()).unwrap()
 }
 
+#[test]
+fn malformed_place_coordinates_are_rejected_instead_of_silently_changed() {
+    let mut s = session();
+    let png = png(4, 2, [20, 40, 60, 255], None);
+    let original = s.doc().unwrap().doc.layers.clone();
+    // Previously filter_map dropped the string from a five-element rectangle and
+    // treated the remaining four values as a different, valid placement.
+    for rect in [json!([0, "ignored", 10, 40, 50]), json!([10, 20, 40, null, 50]), json!([10, 20, 40, 50, 60])] {
+        let mut params = file("tiny.png", &png);
+        params["rect"] = rect;
+        assert!(s.execute("file.place", &params).is_err(), "{params}");
+        assert_eq!(s.doc().unwrap().doc.layers, original, "failed Place must not add art");
+    }
+    // An explicitly supplied invalid position formerly behaved as though no
+    // position were supplied and centred the image on the artboard.
+    for at in [json!(["not-a-number", 20]), json!([10, null]), json!([10, 20, 30]), json!("invalid")] {
+        let mut params = file("tiny.png", &png);
+        params["at"] = at;
+        assert!(s.execute("file.place", &params).is_err(), "{params}");
+        assert_eq!(s.doc().unwrap().doc.layers, original);
+    }
+    let mut params = file("tiny.png", &png);
+    params["rect"] = json!([10, 20, 80, 60]);
+    let placed = s.execute("file.place", &params).unwrap();
+    assert_eq!(placed["ids"].as_array().unwrap().len(), 1);
+    // A null position is no position, as for the other optional params.
+    let mut params = file("tiny.png", &png);
+    params["at"] = Value::Null;
+    assert_eq!(s.execute("file.place", &params).unwrap()["ids"].as_array().unwrap().len(), 1);
+}
+
 #[test]
 fn a_300_px_png_at_300_ppi_places_as_72_pt_centred_selected_and_undoable() {
     let mut s = session();