diff --git a/vllm/v1/attention/backends/gdn_attn.py b/vllm/v1/attention/backends/gdn_attn.py
index 3a2f92d9921c3..ace2cbb0564c8 100644
--- a/vllm/v1/attention/backends/gdn_attn.py
+++ b/vllm/v1/attention/backends/gdn_attn.py
@@ -211,7 +211,7 @@ class GDNAttentionMetadataBuilder(AttentionMetadataBuilder[GDNAttentionMetadata]
                 spec_token_masks = torch.repeat_interleave(
                     spec_sequence_masks, query_lens
                 )
-                index = torch.argsort(spec_token_masks)
+                index = torch.argsort(spec_token_masks, stable=True)
                 num_non_spec_tokens = num_prefill_tokens + num_decode_tokens
                 non_spec_token_indx = index[:num_non_spec_tokens]
                 spec_token_indx = index[num_non_spec_tokens:]