diff --git a/resources/css/components/navigation.css b/resources/css/components/navigation.css
index d8374d15..2db8f579 100644
--- a/resources/css/components/navigation.css
+++ b/resources/css/components/navigation.css
@@ -659,11 +659,13 @@
 /* "Rail transitions from collapsed to expanded should animate the FAB into and out of an extended
  * FAB" — so the header takes one <x-fab label icon> and morphs it, rather than swapping two by
  * `display`, which showed the collapsed one at once while the rail's width was still springing.
- * The label's width springs on the rail's own spatial spring; with the gap closed, what is left is
- * 16px of padding, the 24px icon and 16px again — the 56px square a collapsed FAB is. The label
+ * The label's width springs on the rail's own spatial spring; with the gap closed and the extended
+ * FAB's own minimum width off, `aspect-ratio` squares what is left against the height its size
+ * already sets — 56, 80 or 96px, the three FAB sizes — so no number is repeated here. The label
  * stays in the accessibility tree at both widths, so the FAB keeps its name. Unlayered for the
- * same reason as the rule above: `gap-2` is a utility, and a layer would lose to it. The cap is a
- * transition needs a length to travel to; a rail FAB's label is a word or two. */
+ * same reason as the rule above: `gap-2` and `min-w-20` are utilities, and a layer would lose to
+ * them. The cap is there because a transition needs a length to travel to; a rail FAB's label is a
+ * word or two. */
 [data-navigation-rail-header] [data-fab] > span {
     max-width: 16rem;
     overflow: hidden;
@@ -680,6 +682,8 @@
 
 [data-navigation-rail-header] [data-fab] {
     @variant rail-collapsed {
+        min-width: 0;
+        aspect-ratio: 1;
         gap: 0;
     }
 }
diff --git a/tests/Feature/Components/NavigationRailTest.php b/tests/Feature/Components/NavigationRailTest.php
index 17df10d3..db4b3f3c 100644
--- a/tests/Feature/Components/NavigationRailTest.php
+++ b/tests/Feature/Components/NavigationRailTest.php
@@ -67,21 +67,16 @@ it('takes M3\'s optional divider and turns the container fill off', function ()
         ->toMatch("/\\[data-navigation-rail='collapsible'\\] \\{\\s+width: 6rem;/");
 });
 
-it('flattens a FAB nested in the rail header to elevation 0', function () {
-    $html = (string) $this->blade(<<<'BLADE'
-        <x-navigation-rail mode="expanded">
-            <x-slot:header><x-fab icon="edit" tooltip-right="Compose" /></x-slot:header>
-        </x-navigation-rail>
-        BLADE);
-
-    // The hook the unlayered rules in navigation.css need (N-03).
-    expect($html)->toContain('data-fab');
-
+it('flattens a FAB nested in the rail header and morphs its label', function () {
+    // Both rules hang off `data-fab` on <x-fab>'s root, and both are unlayered, because what they
+    // beat — the FAB's shadow, its gap, an extended FAB's minimum width — are utilities.
     expect(file_get_contents(__DIR__.'/../../../resources/css/components/navigation.css'))
+        // A nested FAB rests at elevation 0, not the 3 a standalone one has (N-03).
         ->toContain('[data-navigation-rail-header] [data-fab],')
         ->toContain('[data-navigation-rail-header] [data-fab]:hover {')
         // One FAB whose label springs shut, not two swapped by display (N-23).
-        ->toContain('[data-navigation-rail-header] [data-fab] > span {');
+        ->toContain('[data-navigation-rail-header] [data-fab] > span {')
+        ->toMatch('/@variant rail-collapsed \{\s+min-width: 0;\s+aspect-ratio: 1;\s+gap: 0;/');
 });
 
 it('draws a destination in both shapes, with its count on the icon and at the end', function () {