diff --git a/qwen_asr/core/transformers_backend/modeling_qwen3_asr.py b/qwen_asr/core/transformers_backend/modeling_qwen3_asr.py
index 75bef86..274595e 100644
--- a/qwen_asr/core/transformers_backend/modeling_qwen3_asr.py
+++ b/qwen_asr/core/transformers_backend/modeling_qwen3_asr.py
@@ -724,11 +724,15 @@ def forward(
             if remainder != 0:
                 cu_chunk_lens += [remainder]
         cu_seqlens = torch.tensor(cu_chunk_lens, device=aftercnn_lens.device).cumsum(-1, dtype=torch.int32)
+        # Build block-diagonal attention mask for non-FA2 backends (SDPA, eager).                                                                                                                                                           
+        # FA2 uses cu_seqlens natively; _prepare_attention_mask returns None for FA2.                                                                                                                                                       
+        attention_mask = self._prepare_attention_mask(hidden_states, cu_seqlens)                                                                                                                                                            
 
         for encoder_layer in self.layers:
             layer_outputs = encoder_layer(
                 hidden_states,
                 cu_seqlens,
+                attention_mask=attention_mask,                                                                                                                                                                                       
             )
 
             hidden_states = layer_outputs[0]