diff --git a/src/layers.h b/src/layers.h
index dedc91c..51603f8 100644
--- a/src/layers.h
+++ b/src/layers.h
@@ -1421,7 +1421,7 @@ namespace chatllm
               sinks(BlockParams::CoreAttentionUseSinks::get() > 0 ?
                     ggml::new_tensor_1d(ctx, ggml::type::GGML_TYPE_F32, BlockParams::CoreAttentionUseSinks::get())
                     : nullptr),
-              pos_helper(helper ? helper : &def_pos_helper)
+              pos_helper(helper ? helper : new BaseTensorPosHelper(max_length))
         {
             allocate_pos_tensor(ctx);
         }