diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index 7d20bf96fc..d5f6e594cf 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -197,6 +197,7 @@
  - [Kenneth Cochran](https://github.com/kennethcochran)
  - [benedikt257](https://github.com/benedikt257)
  - [revam](https://github.com/revam)
+ - [Jxiced](https://github.com/Jxiced)
  - [allesmi](https://github.com/allesmi)
  - [ThunderClapLP](https://github.com/ThunderClapLP)
  - [Shoham Peller](https://github.com/spellr)
diff --git a/Jellyfin.Api/Controllers/StartupController.cs b/Jellyfin.Api/Controllers/StartupController.cs
index 09f20558fe..3bb68553de 100644
--- a/Jellyfin.Api/Controllers/StartupController.cs
+++ b/Jellyfin.Api/Controllers/StartupController.cs
@@ -1,3 +1,4 @@
+using System;
 using System.ComponentModel.DataAnnotations;
 using System.Linq;
 using System.Threading.Tasks;
@@ -131,16 +132,16 @@ public class StartupController : BaseJellyfinApiController
     [ProducesResponseType(StatusCodes.Status204NoContent)]
     public async Task<ActionResult> UpdateStartupUser([FromBody] StartupUserDto startupUserDto)
     {
+        ArgumentNullException.ThrowIfNull(startupUserDto.Name);
+        _userManager.ThrowIfInvalidUsername(startupUserDto.Name);
+
         var user = _userManager.Users.First();
         if (string.IsNullOrWhiteSpace(startupUserDto.Password))
         {
             return BadRequest("Password must not be empty");
         }
 
-        if (startupUserDto.Name is not null)
-        {
-            user.Username = startupUserDto.Name;
-        }
+        user.Username = startupUserDto.Name;
 
         await _userManager.UpdateUserAsync(user).ConfigureAwait(false);
 
diff --git a/Jellyfin.Server.Implementations/Users/UserManager.cs b/Jellyfin.Server.Implementations/Users/UserManager.cs
index 3dfb14d716..4f944c87df 100644
--- a/Jellyfin.Server.Implementations/Users/UserManager.cs
+++ b/Jellyfin.Server.Implementations/Users/UserManager.cs
@@ -744,7 +744,8 @@ namespace Jellyfin.Server.Implementations.Users
             _users[user.Id] = user;
         }
 
-        internal static void ThrowIfInvalidUsername(string name)
+        /// <inheritdoc/>
+        public void ThrowIfInvalidUsername(string name)
         {
             if (!string.IsNullOrWhiteSpace(name) && ValidUsernameRegex().IsMatch(name))
             {
diff --git a/MediaBrowser.Controller/Library/IUserManager.cs b/MediaBrowser.Controller/Library/IUserManager.cs
index 0109cf4b7d..7f06a318ab 100644
--- a/MediaBrowser.Controller/Library/IUserManager.cs
+++ b/MediaBrowser.Controller/Library/IUserManager.cs
@@ -33,6 +33,12 @@ namespace MediaBrowser.Controller.Library
         /// <value>The users ids.</value>
         IEnumerable<Guid> UsersIds { get; }
 
+        /// <summary>
+        /// Checks if the user's username is valid.
+        /// </summary>
+        /// <param name="name">The user's username.</param>
+        void ThrowIfInvalidUsername(string name);
+
         /// <summary>
         /// Initializes the user manager and ensures that a user exists.
         /// </summary>