diff --git a/src/widget/position/span.rs b/src/widget/position/span.rs
index e96a919..dd1f2a6 100644
--- a/src/widget/position/span.rs
+++ b/src/widget/position/span.rs
@@ -60,10 +60,14 @@ impl Widget for Span {
             start.px += self.gap;
         }
 
-        let along = match total.rest == 0.0 && total.rel == 0.0 {
-            true => total,
-            false => Len::default(),
-        };
+        // Carried whole rather than collapsed to one share: a span that sizes
+        // from its children does not resolve `rest`, it passes the weight up,
+        // so nesting spans divides the same space rather than re-dividing a
+        // share of it. Four `rest(1)` children under two spans under one span
+        // get a quarter each, which collapsing to `rest(1)` per level does
+        // not give. Resolution happens at the nearest ancestor with a length,
+        // and the root always has one.
+        let along = total;
         Size::from_axis(axis, along, ortho)
     }
 
diff --git a/tests/layout.rs b/tests/layout.rs
index 6e88906..008c735 100644
--- a/tests/layout.rs
+++ b/tests/layout.rs
@@ -186,3 +186,46 @@ fn only_a_container_that_places_its_children_lengthens_the_chain() {
         "the span above the leaf, and the root the window is held in"
     );
 }
+
+/// A span that sizes from its children passes their `rest` weight up rather
+/// than collapsing it to one share, so nesting divides the same space instead
+/// of re-dividing a share of it.
+#[test]
+fn nested_spans_divide_the_space_once_however_deep_the_nesting_is() {
+    let mut h = Harness::new((400, 200));
+    let (a, b, c, d) = (
+        rect(Color::RED).add(&mut h.rsc),
+        rect(Color::BLUE).add(&mut h.rsc),
+        rect(Color::GREEN).add(&mut h.rsc),
+        rect(Color::WHITE).add(&mut h.rsc),
+    );
+    let left = (a, b).span(Dir::RIGHT).add(&mut h.rsc);
+    let right = (c, d).span(Dir::RIGHT).add(&mut h.rsc);
+    h.set_root((left, right).span(Dir::RIGHT));
+
+    for (i, id) in [a, b, c, d].into_iter().enumerate() {
+        let x = i as f32 * 100.0;
+        assert_corners!(h, id, (x, 0), (x + 100.0, 200));
+    }
+}
+
+/// The same space, unevenly nested: weights carried up mean a share is a
+/// share of the whole, not of whatever branch a widget happens to sit in.
+#[test]
+fn an_uneven_nesting_still_gives_every_share_the_same_length() {
+    let mut h = Harness::new((400, 200));
+    let (a, b, c, d) = (
+        rect(Color::RED).add(&mut h.rsc),
+        rect(Color::BLUE).add(&mut h.rsc),
+        rect(Color::GREEN).add(&mut h.rsc),
+        rect(Color::WHITE).add(&mut h.rsc),
+    );
+    let one = (a,).span(Dir::RIGHT).add(&mut h.rsc);
+    let three = (b, c, d).span(Dir::RIGHT).add(&mut h.rsc);
+    h.set_root((one, three).span(Dir::RIGHT));
+
+    for (i, id) in [a, b, c, d].into_iter().enumerate() {
+        let x = i as f32 * 100.0;
+        assert_corners!(h, id, (x, 0), (x + 100.0, 200));
+    }
+}