diff --git a/python/sglang/srt/entrypoints/openai/protocol.py b/python/sglang/srt/entrypoints/openai/protocol.py
index 9c73e5fad..f7596c975 100644
--- a/python/sglang/srt/entrypoints/openai/protocol.py
+++ b/python/sglang/srt/entrypoints/openai/protocol.py
@@ -317,7 +317,9 @@ class ToolCall(BaseModel):
 
 class ChatCompletionMessageGenericParam(BaseModel):
     role: Literal["system", "assistant", "tool"]
-    content: Union[str, List[ChatCompletionMessageContentTextPart], None]
+    content: Union[str, List[ChatCompletionMessageContentTextPart], None] = Field(
+        default=None
+    )
     tool_call_id: Optional[str] = None
     name: Optional[str] = None
     reasoning_content: Optional[str] = None