diff --git a/returnn/datasets/generating.py b/returnn/datasets/generating.py
index 9b20d1c181..312c970db3 100644
--- a/returnn/datasets/generating.py
+++ b/returnn/datasets/generating.py
@@ -729,6 +729,7 @@ def __init__(self, input_dim, output_dim, num_seqs, seq_len=None,
     """
     if seq_len is None:
       seq_len = {'data': 10, 'classes': 20}
+    self._seq_order = None  # type: typing.Optional[typing.List[int]]
     super(DummyDatasetMultipleSequenceLength, self).__init__(
       input_dim=input_dim,
       output_dim=output_dim,
@@ -756,6 +757,34 @@ def generate_seq(self, seq_idx):
                            for i in range(i1, i2)])
     return DatasetSeq(seq_idx=seq_idx, features=features, targets=targets)
 
+  def get_all_tags(self):
+    """
+    :rtype: list[str]
+    """
+    return ["seq-%i" % i for i in range(self._num_seqs)]
+
+  def init_seq_order(self, epoch=None, seq_list=None, seq_order=None):
+    """
+    If random_shuffle_epoch1, for epoch 1 with "random" ordering, we leave the given order as is.
+    Otherwise, this is mostly the default behavior.
+
+    :param int|None epoch:
+    :param list[str]|None seq_list: List of sequence tags, to set a predefined order.
+    :param list[int]|None seq_order: List of corpus sequence indices, to set a predefined order.
+    :rtype: bool
+    :returns whether the order changed (True is always safe to return)
+    """
+    super(DummyDatasetMultipleSequenceLength, self).init_seq_order(epoch=epoch, seq_list=seq_list, seq_order=seq_order)
+
+    def get_seq_len(i):
+      return self.seq_len['data']
+
+    self._seq_order = self.get_seq_order_for_epoch(epoch, self._num_seqs, get_seq_len=get_seq_len)
+    self._num_seqs = len(self._seq_order)
+
+  def get_current_seq_order(self):
+    return self._seq_order
+
 
 class DummyDatasetMultipleDataKeys(DummyDataset):
   """