diff --git a/backend/models.py b/backend/models.py
index 7970ce41..5b3d8217 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -85,7 +85,7 @@ class GenerationRequest(BaseModel):
     seed: Optional[int] = Field(None, ge=0)
     model_size: Optional[str] = Field(default="1.7B", pattern="^(1\\.7B|0\\.6B|1B|3B)$")
     instruct: Optional[str] = Field(None, max_length=500)
-    engine: Optional[str] = Field(default="qwen", pattern="^(qwen|qwen_custom_voice|luxtts|chatterbox|chatterbox_turbo|tada|kokoro)$")
+    engine: Optional[str] = Field(default=None, pattern="^(qwen|qwen_custom_voice|luxtts|chatterbox|chatterbox_turbo|tada|kokoro)$")
     personality: bool = Field(
         default=False,
         description="When true and the profile has a personality prompt, the input text is rewritten in-character before TTS.",