diff --git a/bayesflow/adapters/transforms/broadcast.py b/bayesflow/adapters/transforms/broadcast.py
index 646e1f72e..562e5029b 100644
--- a/bayesflow/adapters/transforms/broadcast.py
+++ b/bayesflow/adapters/transforms/broadcast.py
@@ -117,7 +117,7 @@ def forward(self, data: dict[str, np.ndarray], **kwargs) -> dict[str, np.ndarray
                 data[k] = np.expand_dims(data[k], axis=tuple(np.arange(0, len_diff)))
             elif self.expand == "right":
                 data[k] = np.expand_dims(data[k], axis=tuple(-np.arange(1, len_diff + 1)))
-            elif isinstance(self.expand, tuple):
+            elif isinstance(self.expand, Sequence):
                 if len(self.expand) is not len_diff:
                     raise ValueError("Length of `expand` must match the length difference of the involed arrays.")
                 data[k] = np.expand_dims(data[k], axis=self.expand)