diff --git a/src/providers/openai.rs b/src/providers/openai.rs
index 6a6d99a..5f256bb 100644
--- a/src/providers/openai.rs
+++ b/src/providers/openai.rs
@@ -137,11 +137,11 @@ impl OpenAIProvider {
                 Value::String(raw) => {
                     // If the string is already valid JSON, keep it as-is
                     // Otherwise, ensure it's a proper JSON string
-                    if serde_json::from_str::<Value>(raw).is_ok() {
+                    if serde_json::from_str::<Value>(&raw).is_ok() {
                         Value::String(raw)
                     } else {
                         // Invalid JSON string - wrap it as a proper JSON string
-                        serde_json::to_string(&raw).unwrap_or_else(|_| "null".to_string())
+                        Value::String(serde_json::to_string(&raw).unwrap_or_else(|_| "null".to_string()))
                     }
                 }
                 value => Value::String(