diff --git a/crates/engine/src/cmd/slices.rs b/crates/engine/src/cmd/slices.rs
index cad1335c1..1adc147c5 100644
--- a/crates/engine/src/cmd/slices.rs
+++ b/crates/engine/src/cmd/slices.rs
@@ -348,8 +348,13 @@ fn from_guides(s: &mut Session, _: &Value) -> Result<Value> {
         v
     };
     let (xs, ys) = (cuts(true, region.x0, region.x1), cuts(false, region.y0, region.y1));
-    let rects: Vec<Rect> =
-        ys.windows(2).flat_map(|y| xs.windows(2).map(move |x| Rect::new(x[0], y[0], x[1], y[1]))).filter(|r| valid_rect(*r)).collect();
+    // One past the limit tells too many, without making every piece of a huge grid first.
+    let rects: Vec<Rect> = ys
+        .windows(2)
+        .flat_map(|y| xs.windows(2).map(move |x| Rect::new(x[0], y[0], x[1], y[1])))
+        .filter(|r| valid_rect(*r))
+        .take(MAX_PIECES + 1)
+        .collect();
     if rects.len() > MAX_PIECES {
         return Err(EngineError::Other(format!("Create from Guides: the guides make more than {MAX_PIECES} slices")));
     }
diff --git a/crates/engine/src/tests/slices.rs b/crates/engine/src/tests/slices.rs
index f14e878d3..eee1a4769 100644
--- a/crates/engine/src/tests/slices.rs
+++ b/crates/engine/src/tests/slices.rs
@@ -86,6 +86,19 @@ fn releasing_a_user_slice_leaves_an_unpainted_rectangle() {
     assert_eq!(s.doc().unwrap().selection.objects, vec![NodeId(rid)]);
 }
 
+/// Guides cutting more pieces than a document takes are refused before the grid is made.
+#[test]
+fn too_many_guide_pieces_are_refused() {
+    let mut s = session();
+    let doc = std::sync::Arc::make_mut(&mut s.doc_mut().unwrap().doc);
+    for i in 1..3000 {
+        for vertical in [true, false] {
+            doc.guides.push(vectorcraft_doc::Guide::new(vertical, f64::from(i) * 0.1));
+        }
+    }
+    assert!(s.execute("object.slice.fromGuides", &json!({})).unwrap_err().to_string().contains("more than"));
+}
+
 #[test]
 fn guides_give_nine_slices() {
     let mut s = session();