diff --git a/vllm/v1/core/single_type_kv_cache_manager.py b/vllm/v1/core/single_type_kv_cache_manager.py
index 0b6b7ed42ac1..b6e0305a312d 100644
--- a/vllm/v1/core/single_type_kv_cache_manager.py
+++ b/vllm/v1/core/single_type_kv_cache_manager.py
@@ -1000,7 +1000,8 @@ def cache_blocks(self, request: Request, num_tokens: int) -> None:
             for block in self.req_to_blocks[request.request_id][
                 num_cached_blocks_before:num_cached_blocks_after
             ]:
-                assert block.block_hash is not None
+                if block.is_null:
+                    continue
                 self.cached_blocks_this_step.add(block.block_hash)
 
     def new_step_starts(self) -> None: