diff --git a/src/Api/Vault/Models/Response/AttachmentResponseModel.cs b/src/Api/Vault/Models/Response/AttachmentResponseModel.cs
index c7e3caabb9e8..f3c0261e9832 100644
--- a/src/Api/Vault/Models/Response/AttachmentResponseModel.cs
+++ b/src/Api/Vault/Models/Response/AttachmentResponseModel.cs
@@ -1,5 +1,4 @@
-using System.Text.Json.Serialization;
-using Bit.Core.Models.Api;
+using Bit.Core.Models.Api;
 using Bit.Core.Settings;
 using Bit.Core.Utilities;
 using Bit.Core.Vault.Entities;
@@ -15,7 +14,7 @@ public AttachmentResponseModel(AttachmentResponseData data) : base("attachment")
         Url = data.Url;
         FileName = data.Data.FileName;
         Key = data.Data.Key;
-        Size = data.Data.Size;
+        Size = data.Data.Size.ToString();
         SizeName = CoreHelpers.ReadableBytesSize(data.Data.Size);
     }
 
@@ -27,7 +26,7 @@ public AttachmentResponseModel(string id, CipherAttachment.MetaData data, Cipher
         Url = $"{globalSettings.Attachment.BaseUrl}/{cipher.Id}/{id}";
         FileName = data.FileName;
         Key = data.Key;
-        Size = data.Size;
+        Size = data.Size.ToString();
         SizeName = CoreHelpers.ReadableBytesSize(data.Size);
     }
 
@@ -35,8 +34,7 @@ public AttachmentResponseModel(string id, CipherAttachment.MetaData data, Cipher
     public string Url { get; set; }
     public string FileName { get; set; }
     public string Key { get; set; }
-    [JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
-    public long Size { get; set; }
+    public string Size { get; set; }
     public string SizeName { get; set; }
 
     public static IEnumerable<AttachmentResponseModel> FromCipher(Cipher cipher, IGlobalSettings globalSettings)