diff --git a/src/Custom/Assistants/MessageCreationAttachment.cs b/src/Custom/Assistants/MessageCreationAttachment.cs
index 521de9c11..d0de2c392 100644
--- a/src/Custom/Assistants/MessageCreationAttachment.cs
+++ b/src/Custom/Assistants/MessageCreationAttachment.cs
@@ -26,7 +26,47 @@ public partial class MessageCreationAttachment
     public IReadOnlyList<ToolDefinition> Tools { get; }
 
     private void SerializeTools(Utf8JsonWriter writer, ModelReaderWriterOptions options)
-        => writer.WriteObjectValue(Tools, options);
+    {
+        if (Tools is null)
+        {
+            writer.WriteNullValue();
+            return;
+        }
+
+        writer.WriteStartArray();
+        foreach (ToolDefinition tool in Tools)
+        {
+            using var ms = new System.IO.MemoryStream();
+            using (var tempWriter = new Utf8JsonWriter(ms))
+            {
+                tempWriter.WriteObjectValue(tool, options);
+                tempWriter.Flush();
+            }
+
+            using (JsonDocument doc = JsonDocument.Parse(ms.ToArray()))
+            {
+                JsonElement root = doc.RootElement;
+                if (root.ValueKind == JsonValueKind.Object)
+                {
+                    writer.WriteStartObject();
+                    foreach (var prop in root.EnumerateObject())
+                    {
+                        if (prop.NameEquals("file_search"u8))
+                        {
+                            continue;
+                        }
+                        prop.WriteTo(writer);
+                    }
+                    writer.WriteEndObject();
+                }
+                else
+                {
+                    root.WriteTo(writer);
+                }
+            }
+        }
+        writer.WriteEndArray();
+    }
 
     private static void DeserializeTools(JsonProperty property, ref IReadOnlyList<ToolDefinition> tools)
     {
diff --git a/tests/Assistants/AssistantsTests.cs b/tests/Assistants/AssistantsTests.cs
index eee6fe503..e90a7b6aa 100644
--- a/tests/Assistants/AssistantsTests.cs
+++ b/tests/Assistants/AssistantsTests.cs
@@ -1,10 +1,3 @@
-using Microsoft.ClientModel.TestFramework;
-using NUnit.Framework;
-using NUnit.Framework.Internal;
-using OpenAI.Assistants;
-using OpenAI.Files;
-using OpenAI.Tests.Utility;
-using OpenAI.VectorStores;
 using System;
 using System.ClientModel;
 using System.ClientModel.Primitives;
@@ -14,6 +7,19 @@
 using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.ClientModel.TestFramework;
+using NUnit.Framework;
+using NUnit.Framework;
+using NUnit.Framework.Internal;
+using NUnit.Framework.Internal;
+using OpenAI.Assistants;
+using OpenAI.Assistants;
+using OpenAI.Files;
+using OpenAI.Files;
+using OpenAI.Tests.Utility;
+using OpenAI.Tests.Utility;
+using OpenAI.VectorStores;
+using OpenAI.VectorStores;
 using static OpenAI.Tests.TestHelpers;
 
 namespace OpenAI.Tests.Assistants;
@@ -30,7 +36,6 @@ public class AssistantsTests : OpenAIRecordedTestBase
     private readonly List<string> _vectorStoreIdsToDelete = [];
 
     private static readonly DateTimeOffset s_2024 = new(2024, 1, 1, 0, 0, 0, TimeSpan.Zero);
-    private static readonly string s_testAssistantName = $".NET SDK Test Assistant - Please Delete Me";
     private static readonly string s_cleanupMetadataKey = $"test_metadata_cleanup_eligible";
 
     private AssistantClient GetTestClient() => GetProxiedOpenAIClient<AssistantClient>(TestScenario.Assistants);
@@ -847,6 +852,45 @@ This file describes the favorite foods of several people.
         });
     }
 
+    [Test]
+    public async Task FileOnMessageWorks()
+    {
+        // First, we need to upload a simple test file.
+        OpenAIFileClient fileClient = GetTestClient<OpenAIFileClient>(TestScenario.Files);
+        OpenAIFile testFile = fileClient.UploadFile(
+            BinaryData.FromString("""
+            This file describes the favorite foods of several people.
+
+            Summanus Ferdinand: tacos
+            Tekakwitha Effie: pizza
+            Filip Carola: cake
+            """).ToStream(),
+            "favorite_foods.txt",
+            FileUploadPurpose.Assistants);
+        Validate(testFile);
+
+        AssistantClient client = GetTestClient();
+
+        var thread = client.CreateThread();
+        var assistant = client.CreateAssistant("gpt-4o-mini");
+
+        var message = await client.CreateMessageAsync(
+        thread.Value.Id,
+        MessageRole.User,
+        new[] {
+            MessageContent.FromText("What is this file?"),
+        },
+        new MessageCreationOptions()
+        {
+            Attachments = [
+                new MessageCreationAttachment(testFile.Id, new List<ToolDefinition>() { ToolDefinition.CreateFileSearch() }),
+                new MessageCreationAttachment(testFile.Id, new List<ToolDefinition>() { ToolDefinition.CreateCodeInterpreter() })
+                ]
+        });
+
+        var result = client.CreateRunStreamingAsync(thread.Value.Id, assistant.Value.Id);
+    }
+
     [Test]
     public async Task FileSearchStreamingWorks()
     {