diff --git a/src/geofabrics/dem.py b/src/geofabrics/dem.py
index fd0a4ca7..10054b40 100644
--- a/src/geofabrics/dem.py
+++ b/src/geofabrics/dem.py
@@ -1749,7 +1749,7 @@ def add_coarse_dems(
                 return False
             # Check for overlap with the Coarse DEM
             chunks = (
-                {"x": chunk_size, "y": chunk_size} if chunk_size is not None else False
+                {"x": chunk_size, "y": chunk_size} if chunk_size is not None else True
             )
             coarse_dem = rioxarray.rioxarray.open_rasterio(
                 coarse_dem_path, masked=True, chunks=chunks