diff --git a/vllm/v1/attention/backends/flash_attn.py b/vllm/v1/attention/backends/flash_attn.py
index ae88acf6b6501..d8ce0d8ed556a 100644
--- a/vllm/v1/attention/backends/flash_attn.py
+++ b/vllm/v1/attention/backends/flash_attn.py
@@ -141,6 +141,10 @@ def forward(
         query = query.view(-1, self.num_heads, self.head_size)
         key = key.view(-1, self.num_kv_heads, self.head_size)
         value = value.view(-1, self.num_kv_heads, self.head_size)
+        assert query.stride(-1) == 1, "Query tensor must be contiguous."
+        assert key.stride(-1) == 1, "Key tensor must be contiguous."
+        assert value.stride(-1) == 1, "Value tensor must be contiguous."
+
         output = torch.empty_like(query)
         torch.ops.vllm.unified_v1_flash_attention(
             output,
@@ -210,23 +214,23 @@ def unified_v1_flash_attention(
         query[:num_actual_tokens],
         key_cache,
         value_cache,
-        None,
+        None,  # out
         attn_metadata.query_start_loc,
         attn_metadata.seq_start_loc,
-        None,
+        None,  # seqused_k
         attn_metadata.block_table,
         alibi_slopes,
         attn_metadata.max_query_len,
         attn_metadata.max_seq_len,
-        0.0,
+        0.0,  # dropout_p
         softmax_scale,
-        False,
-        True,
+        False,  # zero_tensors
+        True,  # causal
         window_size[0],
         window_size[1],
         logits_soft_cap,
-        False,
-        None,
+        False,  # return_softmax
+        None,  # generator
     )[0]
     # TODO(woosuk): Remove this unnecessary copy.
     output[:num_actual_tokens].copy_(attn_output)