diff --git a/vllm/models/deepseek_v4/common/ops/cache_utils.py b/vllm/models/deepseek_v4/common/ops/cache_utils.py
index 6838ef928d..fefc10ec35 100644
--- a/vllm/models/deepseek_v4/common/ops/cache_utils.py
+++ b/vllm/models/deepseek_v4/common/ops/cache_utils.py
@@ -561,6 +561,7 @@ def combine_topk_swa_indices(
         )
     else:
         combined_indices, combined_lens = out
+        combined_indices.fill_(-1)
 
     _COMBINE_TOPK_SWA_INDICES_KERNEL(
         combined_indices,