diff --git a/workflow/rules/flatfield_corr.smk b/workflow/rules/flatfield_corr.smk
index 977e061..82470ec 100644
--- a/workflow/rules/flatfield_corr.smk
+++ b/workflow/rules/flatfield_corr.smk
@@ -79,7 +79,7 @@ rule apply_basic_flatfield_corr:
             allow_missing=True,
         ),
     params:
-        out_chunks=(128, 128, 128),
+        out_chunks=[128, 128, 128],
     output:
         zarr=temp(
             directory(