diff --git a/vllm/v1/spec_decode/eagle.py b/vllm/v1/spec_decode/eagle.py
index 66697132b365..3793a83e74e1 100644
--- a/vllm/v1/spec_decode/eagle.py
+++ b/vllm/v1/spec_decode/eagle.py
@@ -71,7 +71,6 @@ def __init__(
         self.device = device
         self.dtype = vllm_config.model_config.dtype
         self.max_model_len = vllm_config.model_config.max_model_len
-        self.block_size = vllm_config.cache_config.block_size
         self.dp_rank = vllm_config.parallel_config.data_parallel_rank
         self.num_speculative_tokens = self.speculative_config.num_speculative_tokens
         self.max_num_tokens = vllm_config.scheduler_config.max_num_batched_tokens
@@ -470,22 +469,23 @@ def propose(
                 common_attn_metadata._num_computed_tokens_cpu += 1
 
             # Compute the slot mapping.
+            block_size = attn_metadata_builder.kv_cache_spec.block_size
             if self.uses_mrope:
                 # all dimensions of positions are the same
-                block_numbers = clamped_positions[0] // self.block_size
+                block_numbers = clamped_positions[0] // block_size
             else:
-                block_numbers = clamped_positions // self.block_size
+                block_numbers = clamped_positions // block_size
             block_ids = common_attn_metadata.block_table_tensor.gather(
                 dim=1, index=block_numbers.view(-1, 1)
             )
             block_ids = block_ids.view(-1)
             if self.uses_mrope:
                 common_attn_metadata.slot_mapping = (
-                    block_ids * self.block_size + clamped_positions[0] % self.block_size
+                    block_ids * block_size + clamped_positions[0] % block_size
                 )
             else:
                 common_attn_metadata.slot_mapping = (
-                    block_ids * self.block_size + clamped_positions % self.block_size
+                    block_ids * block_size + clamped_positions % block_size
                 )
             # Mask out the slot mappings that exceed the max model length.
             # Otherwise, the KV cache will be inadvertently updated with the
@@ -800,12 +800,11 @@ def propose_tree(
             attn_metadata.seq_lens.masked_fill_(exceeds_max_model_len, 1)
 
             # Compute the slot mapping.
+            block_size = tree_attn_metadata_builder.kv_cache_spec.block_size
             query_positions = flattened_draft_positions[:, level : level + query_len]
-            block_numbers = query_positions // self.block_size
+            block_numbers = query_positions // block_size
             block_ids = attn_metadata.block_table.gather(dim=1, index=block_numbers)
-            slot_mapping = (
-                block_ids * self.block_size + query_positions % self.block_size
-            )
+            slot_mapping = block_ids * block_size + query_positions % block_size
             # Mask out the slot mappings that exceed the max model length.
             # Otherwise, the KV cache will be inadvertently updated with the
             # padding tokens.