diff --git a/OpenTween/ApplicationEvents.cs b/OpenTween/ApplicationEvents.cs
index dd802ac8f..14ed28347 100644
--- a/OpenTween/ApplicationEvents.cs
+++ b/OpenTween/ApplicationEvents.cs
@@ -28,13 +28,11 @@
 #nullable enable
 
 using System;
-using System.Linq;
 using System.Windows.Forms;
 using OpenTween.Connection;
 using OpenTween.Models;
 using OpenTween.Setting;
 using OpenTween.SocialProtocol;
-using OpenTween.SocialProtocol.Twitter;
 
 namespace OpenTween
 {
diff --git a/OpenTween/SocialProtocol/AccountCollection.cs b/OpenTween/SocialProtocol/AccountCollection.cs
index 7bc88235a..8b9e14586 100644
--- a/OpenTween/SocialProtocol/AccountCollection.cs
+++ b/OpenTween/SocialProtocol/AccountCollection.cs
@@ -25,7 +25,6 @@
 using System.Collections.Generic;
 using System.Linq;
 using OpenTween.Models;
-using OpenTween.SocialProtocol.Twitter;
 
 namespace OpenTween.SocialProtocol
 {
@@ -33,7 +32,7 @@ public sealed class AccountCollection : IDisposable
     {
         private Dictionary<AccountKey, ISocialAccount> accounts = new();
         private AccountKey? primaryAccountKey;
-        private readonly ISocialAccount emptyAccount = new TwitterAccount(AccountKey.Empty);
+        private readonly ISocialAccount emptyAccount = new InvalidAccount(AccountKey.Empty);
 
         public bool IsDisposed { get; private set; }
 
diff --git a/OpenTween/SocialProtocol/InvalidAccount.cs b/OpenTween/SocialProtocol/InvalidAccount.cs
index 4c47ac620..bb43bbe16 100644
--- a/OpenTween/SocialProtocol/InvalidAccount.cs
+++ b/OpenTween/SocialProtocol/InvalidAccount.cs
@@ -26,7 +26,6 @@
 using OpenTween.Api;
 using OpenTween.Connection;
 using OpenTween.Models;
-using OpenTween.SocialProtocol.Twitter;
 
 namespace OpenTween.SocialProtocol
 {
@@ -64,6 +63,15 @@ public bool CanUsePostId(PostId postId)
         public void Dispose()
             => this.IsDisposed = true;
 
+        private class InvalidPersonId : PersonId
+        {
+            public override string IdType
+                => "invalid";
+
+            public override string Id
+                => "0";
+        }
+
         private class InvalidAccountConnection : IApiConnection
         {
             public void ThrowIfUnauthorizedScope(string scope)
@@ -135,7 +143,7 @@ private WebApiException CreateException()
         private class InvalidAccountState : ISocialAccountState
         {
             public PersonId UserId
-                => new TwitterUserId("0");
+                => new InvalidPersonId();
 
             public string UserName
                 => "(Unknown account)";