diff --git a/crates/compose/src/lib.rs b/crates/compose/src/lib.rs
index 89ea89bd..e95ebd4b 100644
--- a/crates/compose/src/lib.rs
+++ b/crates/compose/src/lib.rs
@@ -679,10 +679,12 @@ pub fn frame_specs(doc: &Document, sid: StoryId) -> Vec<FrameSpec> {
                 let abs = doc.first_page_of_spread(si) + pi;
                 (Some(doc.page_name(abs)), Some(abs), sp.pages.get(pi).is_some_and(|p| p.side == designcraft_doc::PageSide::Left))
             }
-            (Some(designcraft_doc::SpreadRef::Parent(pi)), Some(sp)) => {
+            (Some(designcraft_doc::SpreadRef::Parent(_)), Some(sp)) => {
                 let prefix = sp.parent.as_ref().map(|p| p.prefix.clone()).unwrap_or_else(|| "A".into());
-                let _ = pi;
-                (Some(prefix), None, false)
+                // The side of the parent page under the frame, so a folio there aligns to the spine of its own page.
+                let under = sp.page_at_x(item.bounds().center().x).and_then(|pi| sp.pages.get(pi));
+                let left = under.is_some_and(|p| p.side == designcraft_doc::PageSide::Left);
+                (Some(prefix), None, left)
             }
             _ => (None, None, false),
         };
diff --git a/crates/compose/src/tests.rs b/crates/compose/src/tests.rs
index 15c412ad..d210a442 100644
--- a/crates/compose/src/tests.rs
+++ b/crates/compose/src/tests.rs
@@ -7310,3 +7310,16 @@ fn rule_above_offset_is_measured_from_the_baseline() {
     assert!((rule.height() - 1.5).abs() < 1e-6);
     assert!(rule.y0 > first.baseline, "the rule stays below the row above: {rule:?}, its baseline {}", first.baseline);
 }
+
+#[test]
+fn parent_page_frames_know_which_side_of_the_spine_they_are_on() {
+    // Folios on a facing-pages parent: towards/away from spine must differ between its left and right page.
+    let mut d = Document::new(&NewDocument::default());
+    let lid = d.default_layer();
+    let w = d.parents[0].pages[0].width;
+    let para = ParaFormat { para: ParaAttrs { align: Some(Align::TowardsSpine), ..Default::default() }, ..Default::default() };
+    let (_, left_story) = d.add_text_frame(SpreadRef::Parent(0), Rect::new(36.0, 700.0, w - 36.0, 730.0), lid, "7", para.clone()).unwrap();
+    let (_, right_story) = d.add_text_frame(SpreadRef::Parent(0), Rect::new(w + 36.0, 700.0, 2.0 * w - 36.0, 730.0), lid, "8", para).unwrap();
+    assert!(frame_specs(&d, left_story)[0].left_page);
+    assert!(!frame_specs(&d, right_story)[0].left_page);
+}