diff --git a/crates/engine/src/media/source.rs b/crates/engine/src/media/source.rs
index 308ca24c1..d49d146a7 100644
--- a/crates/engine/src/media/source.rs
+++ b/crates/engine/src/media/source.rs
@@ -60,12 +60,13 @@ impl SourceLevel {
 /// only part of the photo, so its pixels come from a source that many times larger (the source
 /// level is chosen from this, or a tight crop shown at its own pixels would be a stretched preview).
 /// The crop is bounded as the render bounds it (issue #2555), so one reaching far past the photo
-/// doesn't pick a source too small for the frame it renders.
+/// doesn't pick a source too small for the frame it renders. Its rect is in the photo as shown
+/// (turned by its orientation), so it is measured with the turned size.
 pub(super) fn source_edge_needed(p: &Photo, settings: &DevelopSettings, apply_crop: bool, out_long: usize) -> usize {
     let (w, h) = (f64::from(p.width.max(1)), f64::from(p.height.max(1)));
     let (ow, oh) = if settings.orientation.swaps_axes() { (h, w) } else { (w, h) };
     let r = settings.crop.geometry.bounded(ow, oh).rect;
-    let shown = if apply_crop { (r.width() * w).max(r.height() * h) } else { w.max(h) };
+    let shown = if apply_crop { (r.width() * ow).max(r.height() * oh) } else { w.max(h) };
     if !shown.is_finite() || shown < 1.0 {
         return out_long;
     }
diff --git a/crates/engine/src/media/tests.rs b/crates/engine/src/media/tests.rs
index 8eec0fd03..bf283fb04 100644
--- a/crates/engine/src/media/tests.rs
+++ b/crates/engine/src/media/tests.rs
@@ -389,7 +389,7 @@ fn a_crop_far_past_the_photo_reads_the_source_its_bounded_frame_needs() {
         let mut d = lightcraft_develop::DevelopSettings { orientation, ..Default::default() };
         d.crop.geometry = wild;
         let r = wild.bounded(ow, oh).rect;
-        let expected = (1600.0 * w.max(h) / (r.width() * w).max(r.height() * h)) as usize;
+        let expected = (1600.0 * w.max(h) / (r.width() * ow).max(r.height() * oh)) as usize;
         assert_eq!(super::source::source_edge_needed(&p, &d, true, 1600), expected, "{orientation:?}");
     }
 }
@@ -408,12 +408,20 @@ fn crops_on_the_photo_keep_the_source_size_they_need() {
             for aspect in [None, Some(1.0), Some(3.0), Some(0.25)] {
                 let mut d = lightcraft_develop::DevelopSettings { orientation, ..Default::default() };
                 d.crop.geometry = crop_fit_angle(ow, oh, angle, aspect);
+                // the rect is in the photo as shown, so its pixels are counted in the turned size
                 let r = d.crop.geometry.rect;
-                let expected = (1600.0 * w.max(h) / (r.width() * w).max(r.height() * h)) as usize;
+                let expected = (1600.0 * w.max(h) / (r.width() * ow).max(r.height() * oh)) as usize;
                 assert_eq!(super::source::source_edge_needed(&p, &d, true, 1600), expected, "{orientation:?} {angle} {aspect:?}");
             }
         }
     }
+    // a square crop of the photo turned a quarter is the photo's short side across: shown 2000 px
+    // long it needs more than the 2560 px preview (counted in the unturned size, it asked for 2000)
+    let mut d = lightcraft_develop::DevelopSettings { orientation: Orientation::Rotate90, ..Default::default() };
+    d.crop.geometry = crop_fit_angle(h, w, 0.0, Some(1.0));
+    let needed = super::source::source_edge_needed(&p, &d, true, 2000);
+    assert_eq!(needed, (2000.0 * w.max(h) / w.min(h)) as usize);
+    assert_eq!(SourceLevel::for_size(needed), SourceLevel::Full, "{needed}");
 }
 
 // a window whose spot reads from further away than a render can hold is refused