diff --git a/lightllm/server/core/objs/sampling_params.py b/lightllm/server/core/objs/sampling_params.py
index 959b2b629..872e5d78f 100644
--- a/lightllm/server/core/objs/sampling_params.py
+++ b/lightllm/server/core/objs/sampling_params.py
@@ -114,7 +114,7 @@ def initialize(self, constraint: str, tokenizer):
         ctypes.memmove(self.constraint, constraint_bytes, len(constraint_bytes))
         self.length = len(constraint_bytes)
         try:
-            if self.length > 0:
+            if self.length > 0 and tokenizer is not None:
                 import xgrammar as xgr
 
                 tokenizer_info = xgr.TokenizerInfo.from_huggingface(tokenizer)
@@ -144,7 +144,7 @@ def initialize(self, constraint: str, tokenizer):
         ctypes.memmove(self.constraint, constraint_bytes, len(constraint_bytes))
         self.length = len(constraint_bytes)
         try:
-            if self.length > 0:
+            if self.length > 0 and tokenizer is not None:
                 import xgrammar as xgr
 
                 tokenizer_info = xgr.TokenizerInfo.from_huggingface(tokenizer)
diff --git a/unit_tests/server/core/objs/test_sampling_params.py b/unit_tests/server/core/objs/test_sampling_params.py
index 489f8ae34..ca684274e 100644
--- a/unit_tests/server/core/objs/test_sampling_params.py
+++ b/unit_tests/server/core/objs/test_sampling_params.py
@@ -12,6 +12,8 @@
     STOP_SEQUENCE_MAX_LENGTH,
     REGULAR_CONSTRAINT_MAX_LENGTH,
     ALLOWED_TOKEN_IDS_MAX_LENGTH,
+    JSON_SCHEMA_MAX_LENGTH,
+    GRAMMAR_CONSTRAINT_MAX_LENGTH,
 )
 
 grammar_str = r"""root ::= (expr "=" term)+
@@ -80,20 +82,20 @@ def test_regular_constraint_initialization():
 
 def test_guided_grammar_initialization():
     grammar = GuidedGrammar()
-    grammar.initialize(grammar_str)
+    grammar.initialize(grammar_str, None)
     assert grammar.to_str() == grammar_str
 
     with pytest.raises(AssertionError):
-        grammar.initialize("a" * (REGULAR_CONSTRAINT_MAX_LENGTH + 1))
+        grammar.initialize("a" * (GRAMMAR_CONSTRAINT_MAX_LENGTH + 1), None)
 
 
 def test_guided_json_schema_initialization():
     schema = GuidedJsonSchema()
-    schema.initialize(schema_str)
+    schema.initialize(schema_str, None)
     assert schema.to_str() == schema_str
 
     with pytest.raises(AssertionError):
-        schema.initialize("a" * (REGULAR_CONSTRAINT_MAX_LENGTH + 1))
+        schema.initialize("a" * (JSON_SCHEMA_MAX_LENGTH + 1), None)
 
 
 def test_allowed_token_ids_initialization():