diff --git a/tests/e2e/test-rx-coverage-viewport-e2e.js b/tests/e2e/test-rx-coverage-viewport-e2e.js
index 52baec1e..c334dc66 100644
--- a/tests/e2e/test-rx-coverage-viewport-e2e.js
+++ b/tests/e2e/test-rx-coverage-viewport-e2e.js
@@ -39,17 +39,28 @@ const BASE = process.env.BASE_URL || 'http://localhost:3000';
     async function viewport() {
       return page.evaluate(() => { const m = window.__rxTestMap, c = m.getCenter(); return { lat: c.lat, lng: c.lng, zoom: m.getZoom() }; });
     }
+    // Leaflet keeps the centre as a pixel coordinate, so a centre read back is
+    // only ever accurate to the pixel it landed on. One pixel spans
+    // 360/(256*2^zoom) degrees of longitude: 0.022° at zoom 6, 0.0014° at
+    // zoom 10. The budget below used to be a flat 0.001°, which at zoom 6
+    // demanded 1/20 of a pixel, so any change to the map container's size
+    // moved the pixel centre enough to fail an assertion about the *view*.
+    // For latitude the Mercator scale is this figure times cos(lat), so using
+    // the longitude figure is the looser bound there, deliberately.
+    const degPerPixel = (zoom) => 360 / (256 * Math.pow(2, zoom));
+
     function assertViewport(actual, expected) {
-      // Leaflet projects centers to pixels during invalidateSize/pan, so allow
-      // sub-pixel coordinate rounding while still checking the intended view.
-      assert(Math.abs(actual.lat - expected.lat) < 0.001, JSON.stringify(actual));
-      assert(Math.abs(actual.lng - expected.lng) < 0.001, JSON.stringify(actual));
+      const budget = degPerPixel(expected.zoom);
+      const off = (axis) => axis + ' ' + actual[axis] + ' is more than one pixel ('
+        + budget.toFixed(5) + '°) from ' + expected[axis] + ': ' + JSON.stringify(actual);
+      assert(Math.abs(actual.lat - expected.lat) < budget, off('lat'));
+      assert(Math.abs(actual.lng - expected.lng) < budget, off('lng'));
       assert.equal(actual.zoom, expected.zoom);
     }
     await page.goto(BASE + '/#/rx-coverage'); await waitMap();
     assertViewport(await viewport(), { lat: 12, lng: 34, zoom: 6 });
     await page.evaluate(() => window.__rxTestMap.setView([22, 44], 10, { animate: false }));
-    await page.waitForFunction(() => Math.abs(Number(new URLSearchParams(location.hash.split('?')[1]).get('lat')) - 22) < 0.001);
+    await page.waitForFunction((budget) => Math.abs(Number(new URLSearchParams(location.hash.split('?')[1]).get('lat')) - 22) < budget, degPerPixel(10));
     assertViewport(await page.evaluate(() => JSON.parse(localStorage.getItem('rx-coverage-view'))), { lat: 22, lng: 44, zoom: 10 });
     assert.equal(await page.evaluate(() => localStorage.getItem('map-view')), null, 'coverage must not write the main map\'s saved viewport');
     await page.reload(); await waitMap(); assertViewport(await viewport(), { lat: 22, lng: 44, zoom: 10 });