diff --git a/open-sse/translator/helpers/geminiHelper.js b/open-sse/translator/helpers/geminiHelper.js
index 283d26a5..77be2233 100644
--- a/open-sse/translator/helpers/geminiHelper.js
+++ b/open-sse/translator/helpers/geminiHelper.js
@@ -138,12 +138,16 @@ function convertConstToEnum(obj) {
   }
 }
 
-// Convert enum values to strings (Gemini requires string enum values)
+// Convert enum values to strings (Gemini requires string enum values + explicit type:"string")
 function convertEnumValuesToStrings(obj) {
   if (!obj || typeof obj !== "object") return;
 
   if (obj.enum && Array.isArray(obj.enum)) {
     obj.enum = obj.enum.map(v => String(v));
+    // Gemini API requires type:"string" when enum is present — without it returns 400
+    if (!obj.type) {
+      obj.type = "string";
+    }
   }
 
   for (const value of Object.values(obj)) {