diff --git a/odc/loader/_builder.py b/odc/loader/_builder.py
index 5166de0..cd12e90 100644
--- a/odc/loader/_builder.py
+++ b/odc/loader/_builder.py
@@ -213,9 +213,9 @@ def __call__(
 
         for block_idx in np.ndindex(shape_in_blocks):
             ti, yi, xi = block_idx[0], block_idx[ydim], block_idx[ydim + 1]
-            srcs = []
+            srcs_keys: list[list[tuple[str, int]]] = []
             for _ti in tchunk_range[ti]:
-                srcs.append(
+                srcs_keys.append(
                     [
                         (src_key, src_idx)
                         for src_idx in self.tyx_bins.get((_ti, yi, xi), [])
@@ -225,7 +225,7 @@ def __call__(
 
             dsk[(band_key, *block_idx)] = (
                 _dask_loader_tyx,
-                srcs,
+                srcs_keys,
                 gbt_dask_key,
                 quote((yi, xi)),
                 quote(prefix_dims),