diff --git a/src/lib/__tests__/account-id-port.test.ts b/src/lib/__tests__/account-id-port.test.ts
index 18a826a6..56bd0384 100644
--- a/src/lib/__tests__/account-id-port.test.ts
+++ b/src/lib/__tests__/account-id-port.test.ts
@@ -49,6 +49,14 @@ describe('generateAccountId', () => {
   });
 });
 
+describe('registry entries without a server', () => {
+  it('are skipped instead of throwing', () => {
+    setKnownAccounts([{ id: 'u@example.org@mail.example.org', username: 'u@example.org' } as never]);
+    expect(generateAccountId('u@example.org', 'https://mail.example.org')).toBe('u@example.org@mail.example.org');
+    expect(generateAccountId('u@example.org', 'https://mail.example.org:8443')).toBe('u@example.org@mail.example.org:8443');
+  });
+});
+
 describe('a new default-port account next to a kept host-only id', () => {
   const legacy = { id: 'u@example.org@mail.example.org', username: 'u@example.org', serverUrl: 'https://mail.example.org:8120' };
 
diff --git a/src/lib/account-utils.ts b/src/lib/account-utils.ts
index f60eb6e3..1a445bf5 100644
--- a/src/lib/account-utils.ts
+++ b/src/lib/account-utils.ts
@@ -96,11 +96,13 @@ export function generateAccountId(username: string, serverUrl: string): string {
   if (id === legacy) {
     const explicit = `${id}:${defaultPortOf(serverUrl)}`;
     if (knownAccounts.some((a) => a.id === explicit)) return explicit;
-    const taken = knownAccounts.some((a) => a.id === id && `${a.username}@${serverHostLabel(a.serverUrl)}` !== id);
+    const taken = knownAccounts.some((a) => a.id === id && !!a.serverUrl
+      && `${a.username}@${serverHostLabel(a.serverUrl)}` !== id);
     return taken ? explicit : id;
   }
   const kept = knownAccounts.find((a) => a.id === legacy
     && a.username === username
+    && !!a.serverUrl
     && `${a.username}@${serverHostLabel(a.serverUrl)}` === id);
   return kept ? kept.id : id;
 }