diff --git a/vllm/v1/spec_decode/gemma4.py b/vllm/v1/spec_decode/gemma4.py
index b0a02774faf..7f67ae9f499 100644
--- a/vllm/v1/spec_decode/gemma4.py
+++ b/vllm/v1/spec_decode/gemma4.py
@@ -81,11 +81,16 @@ class Gemma4Proposer(SpecDecodeBaseProposer):
         """
         per_group_attn_metadata: list[object] = []
         per_layer_attn_metadata: dict[str, object] = {}
+        batch_size = common_attn_metadata.batch_size()
         for attn_group in self.draft_attn_groups:
             gid = attn_group.kv_cache_group_id
             if gid in self._per_group_block_tables:
                 cm = copy(common_attn_metadata)
-                cm.block_table_tensor = self._per_group_block_tables[gid]
+                # Slice to actual batch size to match cu_seqlens_q dimension.
+                # The stored block tables may be padded (num_reqs_padded) from
+                # the target forward pass, but the drafter operates on the
+                # unpadded batch.
+                cm.block_table_tensor = self._per_group_block_tables[gid][:batch_size]
             else:
                 cm = common_attn_metadata
             attn_metadata = attn_group.get_metadata_builder().build_for_drafting(