diff --git a/vllm/v1/structured_output/backend_xgrammar.py b/vllm/v1/structured_output/backend_xgrammar.py
index 812c262a2..1ad43d218 100644
--- a/vllm/v1/structured_output/backend_xgrammar.py
+++ b/vllm/v1/structured_output/backend_xgrammar.py
@@ -304,17 +304,17 @@ def validate_xgrammar_grammar(sampling_params: SamplingParams) -> None:
         else:
             schema = so_params.json
 
+        if has_xgrammar_unsupported_json_features(schema):
+            raise ValueError(
+                "The provided JSON schema contains features not supported by xgrammar."
+            )
+
         try:
             xgr.Grammar.from_json_schema(schema)
         except Exception as err:
             raise ValueError(
                 f"Failed to transform json schema into a grammar: {err}"
             ) from err
-
-        if has_xgrammar_unsupported_json_features(schema):
-            raise ValueError(
-                "The provided JSON schema contains features not supported by xgrammar."
-            )
         return
 
     if so_params.grammar: