diff --git a/web/fleet-core.js b/web/fleet-core.js
index edcce4e..a8e344a 100644
--- a/web/fleet-core.js
+++ b/web/fleet-core.js
@@ -206,14 +206,14 @@ export function initMap(elementId, opts = {}) {
           ['==', ['get', 'low_accuracy'], true], '#f59e0b',
           '#0b1220',
         ],
+        // zoom must stay the top-level interpolate input; the low-accuracy
+        // widening goes in the per-stop output (a `case`), since MapLibre
+        // forbids a zoom expression nested inside a `case`.
         'circle-stroke-width': [
-          'case',
-          ['==', ['get', 'low_accuracy'], true], 2.5,
-          ['interpolate', ['linear'], ['zoom'],
-            5, 0.5,
-            12, 1.5,
-            16, 2,
-          ],
+          'interpolate', ['linear'], ['zoom'],
+          5,  ['case', ['==', ['get', 'low_accuracy'], true], 2.5, 0.5],
+          12, ['case', ['==', ['get', 'low_accuracy'], true], 2.5, 1.5],
+          16, ['case', ['==', ['get', 'low_accuracy'], true], 2.5, 2],
         ],
       },
     });