diff --git a/vllm/engine/llm_engine.py b/vllm/engine/llm_engine.py
index d083b962eb282..d735bd60ea9ea 100644
--- a/vllm/engine/llm_engine.py
+++ b/vllm/engine/llm_engine.py
@@ -124,8 +124,8 @@ def __init__(
         # List of (timestamp, num_tokens)
         self.num_generation_tokens: List[Tuple[float, int]] = []
         
-        self.speculative_decoding = True
-        if self.speculative_decoding:
+        self.spec_handler = None
+        if spec_decoding_config is not None:
             self.spec_handler = SpeculativeHandler(spec_decoding_config)
 
     def _init_workers(self, distributed_init_method: str):
@@ -565,7 +565,7 @@ def step(self) -> List[RequestOutput]:
             return ignored
 
         draft_tokens = None
-        if self.speculative_decoding:
+        if self.spec_handler:
             draft_tokens = self.spec_handler.propose()
         
         # Execute the model.
@@ -578,7 +578,7 @@ def step(self) -> List[RequestOutput]:
             draft_tokens=draft_tokens
         )
         
-        if self.speculative_decoding:
+        if self.spec_handler:
             self.spec_handler.accept(output)
             self.spec_handler.invalidate_draft_kv()
             self.spec_handler.invalidate_target_kv()
diff --git a/vllm/sequence.py b/vllm/sequence.py
index ecfaee6e8c3d6..f2e808d9ed926 100644
--- a/vllm/sequence.py
+++ b/vllm/sequence.py
@@ -372,6 +372,10 @@ def __init__(
         self.parent_seq_id = parent_seq_id
         self.output_token = output_token
         self.logprobs = logprobs
+        
+        # only for speculative decoding
+        self.sd_output_tokens = None
+        self.sd_logprobs_list = None
 
     def __repr__(self) -> str:
         return (f"SequenceOutputs(parent_seq_id={self.parent_seq_id}, "