diff --git a/selva_core/ext/synchformer/hf_src/modeling_ast.py b/selva_core/ext/synchformer/hf_src/modeling_ast.py
index 3355bb7..7ee6385 100644
--- a/selva_core/ext/synchformer/hf_src/modeling_ast.py
+++ b/selva_core/ext/synchformer/hf_src/modeling_ast.py
@@ -31,7 +31,32 @@ from transformers.modeling_utils import PreTrainedModel
 try:
     from transformers.pytorch_utils import find_pruneable_heads_and_indices, prune_linear_layer
 except ImportError:
-    from transformers.modeling_utils import find_pruneable_heads_and_indices, prune_linear_layer
+    try:
+        from transformers.modeling_utils import find_pruneable_heads_and_indices, prune_linear_layer
+    except ImportError:
+        # Removed in newer transformers; prune_heads() is never called at inference time.
+        import torch
+        def find_pruneable_heads_and_indices(heads, n_heads, head_size, already_pruned_heads):
+            mask = torch.ones(n_heads, head_size)
+            heads = set(heads) - already_pruned_heads
+            for head in heads:
+                head -= sum(1 if h < head else 0 for h in already_pruned_heads)
+                mask[head] = 0
+            mask = mask.view(-1).contiguous().eq(1)
+            index = torch.arange(len(mask))[mask].long()
+            return heads, index
+
+        def prune_linear_layer(layer, index, dim=0):
+            import torch.nn as nn
+            index = index.to(layer.weight.device)
+            W = layer.weight.index_select(dim, index).clone().detach()
+            new = nn.Linear(W.shape[1], W.shape[0], bias=layer.bias is not None,
+                            device=layer.weight.device, dtype=layer.weight.dtype)
+            new.weight = nn.Parameter(W)
+            if layer.bias is not None:
+                b = layer.bias.index_select(0, index).clone().detach() if dim == 0 else layer.bias.clone().detach()
+                new.bias = nn.Parameter(b)
+            return new
 from transformers.models.audio_spectrogram_transformer.modeling_audio_spectrogram_transformer import ASTConfig
 from transformers.utils import add_code_sample_docstrings, add_start_docstrings, add_start_docstrings_to_model_forward, logging