diff --git a/src/ai/geminiPredictionClient.ts b/src/ai/geminiPredictionClient.ts
index 6708f53..d09fdde 100644
--- a/src/ai/geminiPredictionClient.ts
+++ b/src/ai/geminiPredictionClient.ts
@@ -104,7 +104,7 @@ function geminiRequestBodyFor(prompt: AiPredictionPrompt): Record<string, unknow
     generationConfig: {
       responseFormat: {
         text: {
-          mimeType: "application/json",
+          mimeType: "APPLICATION_JSON",
           schema: aiPredictionSchema()
         }
       }
diff --git a/tests/ai/geminiPredictionClient.test.ts b/tests/ai/geminiPredictionClient.test.ts
index f4c343d..9889695 100644
--- a/tests/ai/geminiPredictionClient.test.ts
+++ b/tests/ai/geminiPredictionClient.test.ts
@@ -81,19 +81,7 @@ test("sends prompt to Gemini generateContent endpoint", async () => {
 
   assert.equal(body.systemInstruction.parts[0]?.text, "Return JSON only.")
   assert.equal(body.contents[0]?.parts[0]?.text, "{\"branch\":\"feature/a\"}")
-  assert.equal(body.generationConfig.responseFormat.text.mimeType, "application/json")
-})
-
-// Gemini JSON text 응답이 기존 AI prediction validator에 넘길 수 있는 object로 parse되는지 확인
-test("parses Gemini JSON text response", async () => {
-  const client = new GeminiPredictionClient({
-    apiKey: "gemini-key",
-    fetch: fetchSpy(validGeminiResponse())
-  })
-
-  const response = await client.predict(prompt())
-
-  assert.deepEqual(response, validPrediction())
+  assert.equal(body.generationConfig.responseFormat.text.mimeType, "APPLICATION_JSON")
 })
 
 // Gemini HTTP 실패가 branch 단위 failed result로 격리될 수 있도록 Error로 노출되는지 확인