diff --git a/python/sglang/srt/managers/router/infer_batch.py b/python/sglang/srt/managers/router/infer_batch.py
index 88e7a1973..61eb8e46d 100644
--- a/python/sglang/srt/managers/router/infer_batch.py
+++ b/python/sglang/srt/managers/router/infer_batch.py
@@ -20,15 +20,16 @@ class FinishReason(IntEnum):
     LENGTH = auto()
     STOP_STR = auto()
 
-    def to_str(self):
-        if self == FinishReason.EOS_TOKEN:
+    @staticmethod
+    def to_str(reason):
+        if reason == FinishReason.EOS_TOKEN:
             return None
-        elif self == FinishReason.LENGTH:
+        elif reason == FinishReason.LENGTH:
             return "length"
-        elif self == FinishReason.STOP_STR:
+        elif reason == FinishReason.STOP_STR:
             return "stop"
         else:
-            raise ValueError(f"Invalid finish reason: {self}")
+            return None
 
 
 class Req:
diff --git a/python/sglang/srt/managers/router/model_rpc.py b/python/sglang/srt/managers/router/model_rpc.py
index d94d3997c..a4d84a6c7 100644
--- a/python/sglang/srt/managers/router/model_rpc.py
+++ b/python/sglang/srt/managers/router/model_rpc.py
@@ -24,7 +24,7 @@ from sglang.srt.managers.io_struct import (
     FlushCacheReq,
     TokenizedGenerateReqInput,
 )
-from sglang.srt.managers.router.infer_batch import Batch, ForwardMode, Req
+from sglang.srt.managers.router.infer_batch import Batch, ForwardMode, Req, FinishReason
 from sglang.srt.managers.router.model_runner import ModelRunner
 from sglang.srt.managers.router.radix_cache import RadixCache
 from sglang.srt.managers.router.scheduler import Scheduler
@@ -615,7 +615,7 @@ class ModelRpcServer:
                     + len(req.output_ids)
                     - req.prompt_tokens,
                     "completion_tokens_wo_jump_forward": req.completion_tokens_wo_jump_forward,
-                    "finish_reason": req.finish_reason.to_str(),
+                    "finish_reason": FinishReason.to_str(req.finish_reason),
                     "hit_stop_str": req.hit_stop_str,
                 }
                 if req.return_logprob: