diff --git a/fastkernels/validate/bench_sglang.py b/fastkernels/validate/bench_sglang.py
index b344616..f6ec20d 100644
--- a/fastkernels/validate/bench_sglang.py
+++ b/fastkernels/validate/bench_sglang.py
@@ -196,7 +196,12 @@ def main():
 
         from sglang.srt.server_args import ServerArgs as _ServerArgs
 
-        _fields = {f.name for f in _dc.fields(_ServerArgs)}
+        # SGLang >= 0.5.20 made ServerArgs a msgspec Struct, which
+        # dataclasses.fields() rejects.
+        if _dc.is_dataclass(_ServerArgs):
+            _fields = {f.name for f in _dc.fields(_ServerArgs)}
+        else:
+            _fields = set(getattr(_ServerArgs, "__struct_fields__", ()))
         if "cuda_graph_max_bs" in _fields:
             engine_kwargs["cuda_graph_max_bs"] = _cg_max_bs
         else: