diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index 540deb86..684fd64c 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -128,6 +128,7 @@ jobs:
           node test-issue-1418-deeplink-hops-channels.js
           node test-issue-1418-polish-review.js
           node test-issue-1420-tile-providers.js
+          node test-issue-1614-tile-url-function.js
           node test-issue-1438-marker-css-vars.js
           node test-issue-1562-observers-summary.js
           node test-issue-1509-nav-active-bg.js
diff --git a/public/roles.js b/public/roles.js
index 96f167b0..66e3a904 100644
--- a/public/roles.js
+++ b/public/roles.js
@@ -374,7 +374,12 @@
         var id = window.MC_getDarkTileProvider();
         var p = window.MC_TILE_PROVIDERS[id];
         if (p && (p.url || p.baseUrl)) {
-          return p.url || p.baseUrl;
+          // #1614: providers added in #1533 (carto/osm/stamen) declare
+          // `url` as a function for lazy config resolution. Invoke it so
+          // we always return a string URL template; L.tileLayer otherwise
+          // stringifies the function source and every tile request 404s.
+          var u = p.url || p.baseUrl;
+          return (typeof u === 'function') ? u() : u;
         }
       }
     } catch (_e) {}
diff --git a/test-all.sh b/test-all.sh
index 6892bc68..004a6dd2 100755
--- a/test-all.sh
+++ b/test-all.sh
@@ -37,6 +37,7 @@ node test-issue-1418-spider-fan.js
 node test-issue-1418-deeplink-hops-channels.js
 node test-issue-1418-polish-review.js
 node test-issue-1420-tile-providers.js
+node test-issue-1614-tile-url-function.js
 node test-issue-1438-marker-css-vars.js
 node test-issue-1438-customizer-mcrole.js
 node test-issue-1446-cb-preset-cascade.js
diff --git a/test-issue-1614-tile-url-function.js b/test-issue-1614-tile-url-function.js
new file mode 100644
index 00000000..b812cf99
--- /dev/null
+++ b/test-issue-1614-tile-url-function.js
@@ -0,0 +1,120 @@
+/* test-issue-1614-tile-url-function.js — regression test for #1614.
+ *
+ * Bug: window.getTileUrl() in public/roles.js returns the provider's
+ * `url` *property as-is*. When the active dark-mode provider declares
+ * `url: function()` (carto/osm/stamen lazy resolvers added in #1533),
+ * the helper returns the function itself. Callers pass that function to
+ * L.tileLayer(), which stringifies the function source as the URL
+ * template — every tile request 404s, the map is blank, no console error.
+ *
+ * Contract under test:
+ *   - getTileUrl() MUST return a string URL template, regardless of
+ *     whether the active provider declares `url` as a string or a function.
+ *   - It must contain the leaflet template placeholders {z}/{x}/{y}.
+ *   - For string-`url` providers it must return the string verbatim
+ *     (so we don't double-invoke or otherwise regress).
+ *
+ * Loads only roles.js — provider registry is mocked directly via
+ * window.MC_TILE_PROVIDERS + window.MC_getDarkTileProvider so the test
+ * stays focused on the consumer (the source of the bug) and would still
+ * fail if map-tile-providers.js drifted.
+ */
+'use strict';
+const vm = require('vm');
+const fs = require('fs');
+const path = require('path');
+const assert = require('assert');
+
+let passed = 0, failed = 0;
+function test(name, fn) {
+  try { fn(); passed++; console.log('  ✅ ' + name); }
+  catch (e) { failed++; console.log('  ❌ ' + name + ': ' + e.message); }
+}
+
+function makeSandbox(theme) {
+  const ctx = {
+    console, setTimeout, clearTimeout,
+    JSON, Date, Math, Object, Array, String, Number, Boolean, Set, Map,
+    fetch: () => Promise.resolve({ ok: false, json: () => Promise.resolve({}) }),
+    CustomEvent: function (type, init) { this.type = type; this.detail = (init && init.detail) || null; },
+    document: {
+      documentElement: { getAttribute: () => theme, style: { getPropertyValue: () => '' } },
+      querySelector: () => null,
+      querySelectorAll: () => [],
+      getElementById: () => null,
+      createElement: () => ({ style: {}, appendChild: () => {}, setAttribute: () => {}, addEventListener: () => {} }),
+      addEventListener: () => {},
+      body: { appendChild: () => {}, style: {} },
+      head: { appendChild: () => {} },
+      readyState: 'complete',
+    },
+    window: {
+      addEventListener: () => {},
+      matchMedia: () => ({ matches: theme === 'dark', addEventListener: () => {} }),
+    },
+  };
+  ctx.window.document = ctx.document;
+  ctx.globalThis = ctx;
+  vm.createContext(ctx);
+  const src = fs.readFileSync(path.join(__dirname, 'public', 'roles.js'), 'utf8');
+  vm.runInContext(src, ctx, { filename: 'public/roles.js' });
+  // Mirror window.* back so bare-name refs inside roles.js (TILE_DARK etc.) resolve.
+  for (const k of Object.keys(ctx.window)) if (!(k in ctx)) ctx[k] = ctx.window[k];
+  return ctx;
+}
+
+console.log('── #1614 getTileUrl() must return a string (not a function) ──');
+
+test('dark + provider with url:function → getTileUrl returns string URL template', () => {
+  const ctx = makeSandbox('dark');
+  ctx.window.MC_TILE_PROVIDERS = {
+    'fn-provider': {
+      provider: 'carto',
+      label: 'Fn Provider',
+      url: function () { return 'https://{s}.basemaps.cartocdn.com/dark_all/{z}/{x}/{y}{r}.png'; },
+      attribution: '© OSM © CartoDB',
+    },
+  };
+  ctx.window.MC_getDarkTileProvider = function () { return 'fn-provider'; };
+
+  const out = ctx.window.getTileUrl();
+  assert.strictEqual(typeof out, 'string',
+    'getTileUrl() must return a string, got typeof ' + typeof out +
+    ' (value: ' + String(out).slice(0, 80) + '…)');
+  assert.ok(/\{z\}/.test(out) && /\{x\}/.test(out) && /\{y\}/.test(out),
+    'returned string must be a leaflet URL template with {z}/{x}/{y}; got: ' + out);
+});
+
+test('dark + provider with url:string → getTileUrl returns it verbatim', () => {
+  const ctx = makeSandbox('dark');
+  const STR = 'https://tiles.example.com/dark/{z}/{x}/{y}.png';
+  ctx.window.MC_TILE_PROVIDERS = {
+    'str-provider': { provider: 'carto', label: 'Str', url: STR, attribution: 'x' },
+  };
+  ctx.window.MC_getDarkTileProvider = function () { return 'str-provider'; };
+
+  const out = ctx.window.getTileUrl();
+  assert.strictEqual(out, STR, 'string-url provider must round-trip verbatim');
+});
+
+test('dark + provider with only baseUrl as function → getTileUrl returns string', () => {
+  // Defense-in-depth: roles.js falls back to p.baseUrl when p.url is missing.
+  // Same function/string treatment must apply.
+  const ctx = makeSandbox('dark');
+  ctx.window.MC_TILE_PROVIDERS = {
+    'base-fn': {
+      provider: 'carto', label: 'Base',
+      baseUrl: function () { return 'https://tiles.example.com/{z}/{x}/{y}.png'; },
+      attribution: 'x',
+    },
+  };
+  ctx.window.MC_getDarkTileProvider = function () { return 'base-fn'; };
+
+  const out = ctx.window.getTileUrl();
+  assert.strictEqual(typeof out, 'string',
+    'baseUrl function must also be invoked; got typeof ' + typeof out);
+  assert.ok(/\{z\}/.test(out), 'returned string must contain {z}; got: ' + out);
+});
+
+console.log('\n#1614 getTileUrl() string contract: ' + passed + ' passed, ' + failed + ' failed');
+process.exit(failed === 0 ? 0 : 1);