diff --git a/src/cell_type_mapper/diff_exp/score_utils.py b/src/cell_type_mapper/diff_exp/score_utils.py
index 843d198c..b4b12119 100644
--- a/src/cell_type_mapper/diff_exp/score_utils.py
+++ b/src/cell_type_mapper/diff_exp/score_utils.py
@@ -187,8 +187,10 @@ def read_raw_precomputed_stats(
         precomputed_stats['gene_names'] = json.loads(
             in_file['col_names'][()].decode('utf-8'))
 
-        row_lookup = json.loads(
-            in_file['cluster_to_row'][()].decode('utf-8'))
+        row_lookup = _read_cluster_to_row(
+            json.loads(
+                in_file['cluster_to_row'][()].decode('utf-8'))
+            )
 
         all_keys = set(['n_cells', 'sum', 'sumsq', 'gt0', 'gt1', 'ge1'])
         all_keys = list(all_keys.intersection(set(in_file.keys())))
@@ -286,13 +288,13 @@ def aggregate_stats(
             sumsq_arr += these_stats['sumsq']
 
         if 'gt0' in these_stats:
-            gt0 += these_stats['gt0']
+            gt0 += list(map(int, these_stats['gt0']))
 
         if 'gt1' in these_stats:
-            gt1 += these_stats['gt1']
+            gt1 += list(map(int, these_stats['gt1']))
 
         if 'ge1' in these_stats:
-            ge1 += these_stats['ge1']
+            ge1 += list(map(int, these_stats['ge1']))
         else:
             has_ge1 = False
 
@@ -317,3 +319,24 @@ def aggregate_stats(
             result[k] = result[k].astype(new_dtype)
 
     return result
+
+
+def _read_cluster_to_row(cluster_row_lookup):
+    """
+    Take cluster row lookup dict.
+    Return cluster row lookup dict with int casted values.
+
+    Parameters
+    ----------
+    cluster_row_lookup: 
+        A dictionary mapping cluster names to index values 
+        for looking up n_cells for a given cluster.
+
+    Returns
+    -------
+    cluster_to_row
+    """
+    cluster_to_row = {}
+    for cluster, row in cluster_row_lookup.items():
+        cluster_to_row[cluster] = int(row)
+    return cluster_to_row
\ No newline at end of file
diff --git a/src/cell_type_mapper/utils/output_utils.py b/src/cell_type_mapper/utils/output_utils.py
index 293d2f1d..22908cd7 100644
--- a/src/cell_type_mapper/utils/output_utils.py
+++ b/src/cell_type_mapper/utils/output_utils.py
@@ -555,7 +555,7 @@ def precomputed_stats_to_uns(
 
 def uns_to_precomputed_stats(
         h5ad_path,
-        uns_key,
+        uns_keys_list,
         tmp_dir=None):
     """
     Read a serialized precomputed stats file from the uns element
@@ -593,7 +593,10 @@ def uns_to_precomputed_stats(
         ['n_cells', 'sum', 'sumsq', 'ge1', 'gt1', 'gt0']
     )
 
-    serialized_data = read_uns_from_h5ad(h5ad_path)[uns_key]
+    serialized_data = read_uns_from_h5ad(h5ad_path)
+    for uns_key in uns_keys_list:
+        serialized_data = serialized_data[uns_key]
+
     with h5py.File(h5_path, 'w') as dst:
         for dataset_name in serialized_data:
             data = serialized_data[dataset_name]
diff --git a/tests/utils/test_output_utils.py b/tests/utils/test_output_utils.py
index 3d6d0b47..7ec5e0de 100644
--- a/tests/utils/test_output_utils.py
+++ b/tests/utils/test_output_utils.py
@@ -468,9 +468,11 @@ def test_re_order_blob(tmp_dir_fixture):
     assert len(new_blob) == len(results_lookup)
 
 
+@pytest.mark.parametrize('nested_uns', [True, False])
 def test_precomputed_stats_to_uns(
         tmp_dir_fixture,
-        precomputed_stats_fixture):
+        precomputed_stats_fixture, 
+        nested_uns):
     """
     Test utility functions to move precomputed stats data from HDF5 to
     the uns element of an h5ad file and back.
@@ -507,16 +509,26 @@ def test_precomputed_stats_to_uns(
     a_data.write_h5ad(h5ad_path)
 
     uns_key = 'serialization_test'
+    uns_key_nested = 'serialization_test_nested'
 
     precomputed_stats_to_uns(
         precomputed_stats_path=precomputed_stats_fixture,
         h5ad_path=h5ad_path,
         uns_key=uns_key)
 
-    roundtrip_path = uns_to_precomputed_stats(
-        uns_key=uns_key,
-        h5ad_path=h5ad_path,
-        tmp_dir=tmp_dir_fixture)
+    if not nested_uns:
+        roundtrip_path = uns_to_precomputed_stats(
+            uns_keys_list=[uns_key],
+            h5ad_path=h5ad_path,
+            tmp_dir=tmp_dir_fixture)
+    else:
+        a_data = anndata.read_h5ad(h5ad_path)
+        a_data.uns[uns_key] = {uns_key_nested: a_data.uns[uns_key]}
+        a_data.write_h5ad(h5ad_path)
+        roundtrip_path = uns_to_precomputed_stats(
+            uns_keys_list=[uns_key, uns_key_nested],
+            h5ad_path=h5ad_path,
+            tmp_dir=tmp_dir_fixture)
 
     with h5py.File(precomputed_stats_fixture, 'r') as expected_src:
         with h5py.File(roundtrip_path, 'r') as actual_src:
@@ -540,3 +552,4 @@ def test_precomputed_stats_to_uns(
         original_uns['maybe'],
         roundtrip_h5ad.uns['maybe']
     )
+