diff --git a/image_prediction/stitching/merging.py b/image_prediction/stitching/merging.py
index d7b8c7e..0892ba7 100644
--- a/image_prediction/stitching/merging.py
+++ b/image_prediction/stitching/merging.py
@@ -78,8 +78,8 @@ def make_merger_aggregator(axis) -> Callable[[Iterable[ImageMetadataPair]], Iter
         # Requires H to be the least element in image-concatenation direction by c1, since the concatenation happens
         # only in c1 -> c2 direction.
         pairs = sorted(pairs, key=c1_getter)
-        aggregation_pair, pairs = juxt(first, rest)(pairs)
-        return list(reduce(merge_on_head_and_aggregate_in_tail, pairs, [aggregation_pair]))
+        head_pair, pairs = juxt(first, rest)(pairs)
+        return list(reduce(merge_on_head_and_aggregate_in_tail, pairs, [head_pair]))
 
     c1_getter = make_coord_getter(f"{axis}1")
     c2_getter = make_coord_getter(f"{axis}2")