diff --git a/pixi.lock b/pixi.lock
index c85c41a..7da5669 100644
--- a/pixi.lock
+++ b/pixi.lock
@@ -861,6 +861,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/noarch/flake8-7.3.0-pyhd8ed1ab_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/fonttools-4.61.1-pyh7db6752_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/fqdn-1.5.1-pyhd8ed1ab_1.conda
+      - conda: https://conda.anaconda.org/conda-forge/noarch/fsspec-2026.9.0-pyhd8ed1ab_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/h11-0.16.0-pyhcf101f3_1.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/h2-4.3.0-pyhcf101f3_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/hpack-4.1.0-pyhd8ed1ab_0.conda
@@ -987,6 +988,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/noarch/flake8-7.3.0-pyhd8ed1ab_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/fonttools-4.61.1-pyh7db6752_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/fqdn-1.5.1-pyhd8ed1ab_1.conda
+      - conda: https://conda.anaconda.org/conda-forge/noarch/fsspec-2026.9.0-pyhd8ed1ab_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/h11-0.16.0-pyhcf101f3_1.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/h2-4.3.0-pyhcf101f3_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/hpack-4.1.0-pyhd8ed1ab_0.conda
@@ -1224,6 +1226,7 @@ environments:
       - conda: https://conda.anaconda.org/conda-forge/noarch/flake8-7.3.0-pyhd8ed1ab_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/fonttools-4.61.1-pyh7db6752_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/fqdn-1.5.1-pyhd8ed1ab_1.conda
+      - conda: https://conda.anaconda.org/conda-forge/noarch/fsspec-2026.9.0-pyhd8ed1ab_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/h11-0.16.0-pyhcf101f3_1.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/h2-4.3.0-pyhcf101f3_0.conda
       - conda: https://conda.anaconda.org/conda-forge/noarch/hpack-4.1.0-pyhd8ed1ab_0.conda
@@ -3470,6 +3473,18 @@ packages:
   - pkg:pypi/fqdn?source=hash-mapping
   size: 16705
   timestamp: 1733327494780
+- conda: https://conda.anaconda.org/conda-forge/noarch/fsspec-2026.9.0-pyhd8ed1ab_0.conda
+  sha256: 7d17272012e7479ba58f8a72b522d3e88e6837a04a111a278ff417aa82364255
+  md5: 42de5cd170647599a84f468a42fabb89
+  depends:
+  - python >=3.11
+  license: BSD-3-Clause
+  license_family: BSD
+  purls:
+  - pkg:pypi/fsspec?source=compressed-mapping
+  run_exports: {}
+  size: 163722
+  timestamp: 1790256848815
 - conda: https://conda.anaconda.org/conda-forge/noarch/h11-0.16.0-pyhcf101f3_1.conda
   sha256: 96cac6573fd35ae151f4d6979bab6fbc90cb6b1fb99054ba19eb075da9822fcb
   md5: b8993c19b0c32a2f7b66cbb58ca27069
diff --git a/pyproject.toml b/pyproject.toml
index d9e82a4..3623603 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -138,5 +138,6 @@ shapely = "*"
 
 [tool.pixi.feature.dev.dependencies]
 flake8 = "*"
+fsspec = "*"
 pytest = ">=4.6"
 pytest-cov = "*"
diff --git a/tests/test_cloud.py b/tests/test_cloud.py
index 7de944e..04941e1 100644
--- a/tests/test_cloud.py
+++ b/tests/test_cloud.py
@@ -8,6 +8,7 @@
 import os
 import shutil
 import numpy as np
+import pytest
 import pointCollection as pc
 from pointCollection.scripts.query_ATL11_cloud import (
     read_ATL11_granule_cloud, read_ATL11_granule_cloud_items)
@@ -106,9 +107,18 @@ def test_read_ATL11_granule_cloud_merges_items(tmp_path):
     assert merged.size == sum(Di.size for Di in items)
 
 
+def test_read_ATL11_granule_cloud_items_missing_index_raises(tmp_path):
+    """by default, a missing index is a staging error"""
+    with pytest.raises(FileNotFoundError, match='missing geoIndex'):
+        read_ATL11_granule_cloud_items(
+            'not-a-real-granule.h5', str(tmp_path / 'no_such_index.h5'), [-1, 1], [-1, 1])
+
+
 def test_read_ATL11_granule_cloud_items_missing_index_returns_none(tmp_path):
-    items = read_ATL11_granule_cloud_items(
-        'not-a-real-granule.h5', str(tmp_path / 'no_such_index.h5'), [-1, 1], [-1, 1])
+    with pytest.warns(UserWarning, match='missing geoIndex'):
+        items = read_ATL11_granule_cloud_items(
+            'not-a-real-granule.h5', str(tmp_path / 'no_such_index.h5'), [-1, 1], [-1, 1],
+            missing_index='skip')
     assert items is None
 
 
diff --git a/tests/test_cloud_paths.py b/tests/test_cloud_paths.py
index a7188b5..09f9f6e 100644
--- a/tests/test_cloud_paths.py
+++ b/tests/test_cloud_paths.py
@@ -200,14 +200,23 @@ def test_remote_index_is_not_reported_missing(tmp_path):
     assert items is not None and len(items) > 0
 
 
+def test_missing_remote_index_raises(tmp_path):
+    """by default, a remote index that really is absent is a staging error"""
+    index_fs = FakeS3FS({})
+    with pytest.raises(FileNotFoundError, match='missing geoIndex'):
+        read_ATL11_granule_cloud_items(
+            'ATL11_044110_0331_007_04.h5', 's3://bucket/no_such_index.h5',
+            [-1, 1], [-1, 1], index_fs=index_fs)
+
+
 def test_missing_remote_index_still_skips(tmp_path):
-    """a remote index that really is absent must still warn and skip"""
+    """with missing_index='skip', an absent remote index must warn and skip"""
     index_fs = FakeS3FS({})
     import warnings
     with warnings.catch_warnings(record=True) as caught:
         warnings.simplefilter('always')
         items = read_ATL11_granule_cloud_items(
             'ATL11_044110_0331_007_04.h5', 's3://bucket/no_such_index.h5',
-            [-1, 1], [-1, 1], index_fs=index_fs)
+            [-1, 1], [-1, 1], index_fs=index_fs, missing_index='skip')
     assert items is None
     assert any('missing geoIndex' in str(w.message) for w in caught)