diff --git a/Cargo.lock b/Cargo.lock
index aea49a0a4..41947aa5a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -470,8 +470,7 @@ dependencies = [
 [[package]]
 name = "async-openai"
 version = "0.28.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "14d76e2f5af19477d6254415acc95ba97c6cc6f3b1e3cb4676b7f0fab8194298"
+source = "git+https://github.com/meilisearch/async-openai?branch=optional-type-function#dd328d4c35ca24c30284c8aff616541ac82eb47a"
 dependencies = [
  "async-openai-macros",
  "backoff",
@@ -496,8 +495,7 @@ dependencies = [
 [[package]]
 name = "async-openai-macros"
 version = "0.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0289cba6d5143bfe8251d57b4a8cac036adf158525a76533a7082ba65ec76398"
+source = "git+https://github.com/meilisearch/async-openai?branch=optional-type-function#dd328d4c35ca24c30284c8aff616541ac82eb47a"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/crates/meilisearch/Cargo.toml b/crates/meilisearch/Cargo.toml
index f7469e7ac..398b62dad 100644
--- a/crates/meilisearch/Cargo.toml
+++ b/crates/meilisearch/Cargo.toml
@@ -112,7 +112,7 @@ utoipa = { version = "5.3.1", features = [
     "openapi_extensions",
 ] }
 utoipa-scalar = { version = "0.3.0", optional = true, features = ["actix-web"] }
-async-openai = "0.28.1"
+async-openai = { git = "https://github.com/meilisearch/async-openai", branch = "optional-type-function" }
 actix-web-lab = { version = "0.24.1", default-features = false }
 
 [dev-dependencies]
diff --git a/crates/meilisearch/src/routes/chat.rs b/crates/meilisearch/src/routes/chat.rs
index 8d07342c8..7869b677d 100644
--- a/crates/meilisearch/src/routes/chat.rs
+++ b/crates/meilisearch/src/routes/chat.rs
@@ -86,7 +86,9 @@ fn setup_search_tool(chat_completion: &mut CreateChatCompletionRequest, prompts:
                                 "description": prompts.search_index_uid_param,
                             },
                             "q": {
-                                "type": ["string", "null"],
+                                // Unfortunately, Mistral does not support an array of types, here.
+                                // "type": ["string", "null"],
+                                "type": "string",
                                 "description": prompts.search_q_param,
                             }
                         },
@@ -269,7 +271,6 @@ async fn streamed_chat(
 
         'main: loop {
             let mut response = client.chat().create_stream(chat_completion.clone()).await.unwrap();
-
             while let Some(result) = response.next().await {
                 match result {
                     Ok(resp) => {
@@ -306,12 +307,14 @@ async fn streamed_chat(
                                         function.as_ref().unwrap();
                                     global_tool_calls
                                         .entry(*index)
+                                        .and_modify(|call| {
+                                            call.append(arguments.as_ref().unwrap());
+                                        })
                                         .or_insert_with(|| Call {
                                             id: id.as_ref().unwrap().clone(),
                                             function_name: name.as_ref().unwrap().clone(),
                                             arguments: arguments.as_ref().unwrap().clone(),
-                                        })
-                                        .append(arguments.as_ref().unwrap());
+                                        });
                                 }
                             }
                             None if !global_tool_calls.is_empty() => {
@@ -322,7 +325,7 @@ async fn streamed_chat(
                                         .into_values()
                                         .map(|call| ChatCompletionMessageToolCall {
                                             id: call.id,
-                                            r#type: ChatCompletionToolType::Function,
+                                            r#type: Some(ChatCompletionToolType::Function),
                                             function: FunctionCall {
                                                 name: call.function_name,
                                                 arguments: call.arguments,
@@ -400,8 +403,9 @@ async fn streamed_chat(
                             None => (),
                         }
                     }
-                    Err(_err) => {
+                    Err(err) => {
                         // writeln!(lock, "error: {err}").unwrap();
+                        tracing::error!("{err:?}");
                     }
                 }
             }