diff --git a/src/dualip/utils/sparse_utils.py b/src/dualip/utils/sparse_utils.py
index 36a0948..a09287d 100644
--- a/src/dualip/utils/sparse_utils.py
+++ b/src/dualip/utils/sparse_utils.py
@@ -285,9 +285,9 @@ def split_csc_by_cols(M: torch.Tensor, split_sizes: List[int]) -> List[torch.Ten
         end_nnz = int(col_ptr[end_col].item())
 
         # slice out the per-block CSC arrays
-        sub_col_ptr = col_ptr[start_col : (end_col + 1)] - col_ptr[start_col]
-        sub_row_idx = row_idx[start_nnz:end_nnz]
-        sub_vals = vals[start_nnz:end_nnz]
+        sub_col_ptr = (col_ptr[start_col : (end_col + 1)] - col_ptr[start_col]).clone()
+        sub_row_idx = row_idx[start_nnz:end_nnz].clone()
+        sub_vals = vals[start_nnz:end_nnz].clone()
 
         # build the sub‐matrix
         M_block = torch.sparse_csc_tensor(sub_col_ptr, sub_row_idx, sub_vals, size=(m, width))