diff --git a/async-openai/src/types/impls.rs b/async-openai/src/types/impls.rs
index 631e5fe5..57f060ac 100644
--- a/async-openai/src/types/impls.rs
+++ b/async-openai/src/types/impls.rs
@@ -351,13 +351,14 @@ impl_from_for_array_of_integer_array!(u16, Prompt);
 
 impl From<&str> for ChatCompletionFunctionCall {
     fn from(value: &str) -> Self {
-        ChatCompletionFunctionCall::String(value.to_string())
+        match value {
+            "none" => Self::None,
+            "auto" => Self::Auto,
+            _ => Self::Function { name: value.to_string() },
+        }
     }
 }
 
-impl From<serde_json::Value> for ChatCompletionFunctionCall {
-    fn from(value: serde_json::Value) -> Self {
-        ChatCompletionFunctionCall::Object(value)
     }
 }
 
diff --git a/async-openai/src/types/types.rs b/async-openai/src/types/types.rs
index 6f569cac..22676197 100644
--- a/async-openai/src/types/types.rs
+++ b/async-openai/src/types/types.rs
@@ -37,11 +37,14 @@ pub enum Stop {
     StringArray(Vec<String>), // minItems: 1; maxItems: 4
 }
 
-#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
-#[serde(untagged)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum ChatCompletionFunctionCall {
-    String(String),
-    Object(serde_json::Value),
+    /// The model does not call a function, and responds to the end-user.
+    None,
+    /// The model can pick between an end-user or calling a function.
+    Auto,
+    /// Forces the model to call the specified function.
+    Function { name : String },
 }
 
 #[derive(Clone, Serialize, Default, Debug, Builder, PartialEq)]