diff --git a/sgkit/io/vcfzarr_reader.py b/sgkit/io/vcfzarr_reader.py
index 8432195cb..7283851b1 100644
--- a/sgkit/io/vcfzarr_reader.py
+++ b/sgkit/io/vcfzarr_reader.py
@@ -61,9 +61,11 @@ def read_vcfzarr(path: PathType) -> xr.Dataset:
     )
 
     # Add a mask for variant ID
+    # Note: we wrap the "." inside a list to workaround https://github.com/dask/dask/issues/6631,
+    #       and therefor force dask array's eq
     ds["variant_id_mask"] = (
         [DIM_VARIANT],
-        variants_id == ".",
+        variants_id == ["."],
     )
 
     return ds