diff --git a/crates/open_router/src/open_router.rs b/crates/open_router/src/open_router.rs
index 4128426a7fb429337028b03c12e90c6395651f0e..3e6e406d9842d5996f2e866d534094ded23fd61c 100644
--- a/crates/open_router/src/open_router.rs
+++ b/crates/open_router/src/open_router.rs
@@ -153,11 +153,12 @@ pub struct RequestUsage {
 }
 
 #[derive(Debug, Serialize, Deserialize)]
-#[serde(untagged)]
+#[serde(rename_all = "lowercase")]
 pub enum ToolChoice {
     Auto,
     Required,
     None,
+    #[serde(untagged)]
     Other(ToolDefinition),
 }