diff --git a/src/library/controller.js b/src/library/controller.js
index fffafb1f2..6be6d29ca 100644
--- a/src/library/controller.js
+++ b/src/library/controller.js
@@ -257,10 +257,16 @@ export function createDataLibrary({
   }
   shareLink?.setLibraryShareListener?.(applyShare);
 
+  // The URL carries what is on. Until availability loads (or when it never
+  // does) that is still what the page opened with, so a hash write in the
+  // meantime keeps it; an entry this instance cannot serve stays in it too.
   shareLink?.setLibraryParamsEncoder?.((params) =>
     encodeLibraryParam(
       params,
-      selection.on.filter((id) => isRegistered(id)),
+      loaded
+        ? selection.on
+        : ((queuedShare ? idsForTokens(queuedShare) : openingShare()) ??
+            readStoredLibrarySelection(storage, switchable).on),
       tokens.tokenById,
     ),
   );
diff --git a/src/library/controller.test.mjs b/src/library/controller.test.mjs
index 9aac21764..51daf7f2a 100644
--- a/src/library/controller.test.mjs
+++ b/src/library/controller.test.mjs
@@ -480,6 +480,40 @@ test('a layer that fails to tear down stays in the library', async (t) => {
   library.destroy();
 });
 
+test('the URL keeps the opening lib= before availability loads and for entries it cannot serve', async (t) => {
+  const manager = sealedManager(t);
+  const shareLink = shareLinkDouble();
+  let answer;
+  const pending = new Promise((resolve) => {
+    answer = resolve;
+  });
+  const library = createDataLibrary({
+    entries,
+    ledger,
+    dataManager: manager,
+    services: {},
+    storage: memoryStorage(),
+    shareLink,
+    initialHash: '#lat=1&lon=2&lib=00.01',
+    source: { ...source({}), getAvailability: () => pending },
+  });
+  const started = library.start();
+  // A camera move rewrites the hash before the catalog answers.
+  assert.equal(shareLink.encode(), '00.01');
+  answer({
+    server: false,
+    availability: new Map([
+      ['night-lights', { available: false, reason: 'server-unavailable' }],
+      ['sea-marks', { available: true, reason: null }],
+    ]),
+  });
+  await started;
+  await manager.waitForLayerSettled?.('lib-sea-marks');
+  assert.equal(manager.layers.has('lib-night-lights'), false);
+  assert.equal(shareLink.encode(), '00.01');
+  library.destroy();
+});
+
 test('zoom flies to an added layer through the caller, reset removes everything', async (t) => {
   const manager = sealedManager(t);
   const storage = memoryStorage();