diff --git a/src/h3/api/basic_int/__init__.py b/src/h3/api/basic_int/__init__.py
index 1086a632..ef827925 100644
--- a/src/h3/api/basic_int/__init__.py
+++ b/src/h3/api/basic_int/__init__.py
@@ -474,8 +474,6 @@ def uncompact_cells(cells, res):
     -----
     There is currently no guaranteed order of the output cells.
     """
-    # TODO: add test to make sure an error is returned when input contains cell
-    # smaller than output res.
 
     hc = _in_collection(cells)
     hu = _cy.uncompact_cells(hc, res)
diff --git a/tests/test_lib/test_cells_and_edges.py b/tests/test_lib/test_cells_and_edges.py
index 4b8e1075..77e8f5ed 100644
--- a/tests/test_lib/test_cells_and_edges.py
+++ b/tests/test_lib/test_cells_and_edges.py
@@ -755,3 +755,13 @@ def test_construct_cell_inverses_int_api():
 def test_center_child_with_deconstruct():
     for h in h3.get_res0_cells():
         h3.construct_cell(*h3.deconstruct_cell(h), 0) == h3.cell_to_center_child(h)
+
+
+def test_uncompact_cells_invalid_resolution():
+    # Create a valid cell at resolution 5
+    h_res5 = h3.latlng_to_cell(0, 0, 5)
+
+    # Attempting to uncompact to a coarser resolution (4)
+    # should raise an H3ResMismatchError
+    with pytest.raises(H3ResMismatchError):
+        h3.uncompact_cells({h_res5}, 4)