diff --git a/masque/file/gdsii.py b/masque/file/gdsii.py
index f589ad8..116fa07 100644
--- a/masque/file/gdsii.py
+++ b/masque/file/gdsii.py
@@ -637,6 +637,7 @@ def check_valid_names(
         max_length: Max allowed length
 
     """
+    names = tuple(names)
     allowed_chars = set(string.ascii_letters + string.digits + '_?$')
 
     bad_chars = [
diff --git a/masque/test/test_gdsii.py b/masque/test/test_gdsii.py
index 7ce8c88..7a2f5b1 100644
--- a/masque/test/test_gdsii.py
+++ b/masque/test/test_gdsii.py
@@ -1,8 +1,10 @@
 from pathlib import Path
 from typing import cast
 import numpy
+import pytest
 from numpy.testing import assert_equal, assert_allclose
 
+from ..error import LibraryError
 from ..pattern import Pattern
 from ..library import Library
 from ..file import gdsii
@@ -69,3 +71,10 @@ def test_gdsii_annotations(tmp_path: Path) -> None:
     read_ann = read_lib["cell"].shapes[(1, 0)][0].annotations
     assert read_ann is not None
     assert read_ann["1"] == ["hello"]
+
+
+def test_gdsii_check_valid_names_validates_generator_lengths() -> None:
+    names = (name for name in ("a" * 40,))
+
+    with pytest.raises(LibraryError, match="invalid names"):
+        gdsii.check_valid_names(names)