diff --git a/returnn/tf/layers/basic.py b/returnn/tf/layers/basic.py
index 79814eee8..9c20e2bde 100644
--- a/returnn/tf/layers/basic.py
+++ b/returnn/tf/layers/basic.py
@@ -6001,7 +6001,6 @@ def get_out_data_from_opts(cls, num_pieces, sources, name, out_dim=None, **kwarg
     assert out.have_feature_axis()
     assert not out.sparse
     assert out.dim % num_pieces == 0
-    dim = out.dim // num_pieces
     out_dim_ = out.feature_dim_or_sparse_dim // num_pieces
     if out_dim:
       out_dim_.declare_same_as(out_dim)