diff --git a/src/grits.py b/src/grits.py
index c9d48280e..c919f6004 100644
--- a/src/grits.py
+++ b/src/grits.py
@@ -226,8 +226,8 @@ def iou(bbox1, bbox2):
     """
     Compute the intersection-over-union of two bounding boxes.
     """
-    intersection = Rect(bbox1).intersect(bbox2)
-    union = Rect(bbox1).include_rect(bbox2)
+    intersection = Rect(list(bbox1)).intersect(list(bbox2))
+    union = Rect(list(bbox1)).include_rect(list(bbox2))
     
     union_area = union.get_area()
     if union_area > 0:
@@ -249,7 +249,7 @@ def cells_to_grid(cells, key='bbox'):
         return [[]]
     num_rows = max([max(cell['row_nums']) for cell in cells])+1
     num_columns = max([max(cell['column_nums']) for cell in cells])+1
-    cell_grid = np.zeros((num_rows, num_columns)).tolist()
+    cell_grid = [["" for _ in range(num_columns)] for _ in range(num_rows)]
     for cell in cells:
         for row_num in cell['row_nums']:
             for column_num in cell['column_nums']:
@@ -267,7 +267,7 @@ def cells_to_relspan_grid(cells):
         return [[]]
     num_rows = max([max(cell['row_nums']) for cell in cells])+1
     num_columns = max([max(cell['column_nums']) for cell in cells])+1
-    cell_grid = np.zeros((num_rows, num_columns)).tolist()
+    cell_grid = [[[0, 0, 0, 0] for _ in range(num_columns)] for _ in range(num_rows)] 
     for cell in cells:
         min_row_num = min(cell['row_nums'])
         min_column_num = min(cell['column_nums'])