diff --git a/odc/loader/testing/mem_reader.py b/odc/loader/testing/mem_reader.py
index 6b294fb..b00977c 100644
--- a/odc/loader/testing/mem_reader.py
+++ b/odc/loader/testing/mem_reader.py
@@ -11,7 +11,7 @@
 import fsspec
 import numpy as np
 import xarray as xr
-from odc.geo.geobox import GeoBox
+from odc.geo.geobox import GeoBox, GeoBoxBase
 from odc.geo.xr import ODCExtensionDa, ODCExtensionDs, xr_coords, xr_reproject
 
 from ..types import (
@@ -148,7 +148,7 @@ class Context:
 
     def __init__(
         self,
-        geobox: GeoBox,
+        geobox: None | GeoBoxBase,
         chunks: None | dict[str, int],
     ) -> None:
         self.geobox = geobox