diff --git a/pyproject.toml b/pyproject.toml
index 77d0f55..968f8d9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -14,6 +14,7 @@ distributed = {version = "^2024.5.0", optional = true, extras = ["testing"]}
 cacheout = "^0.16.0"
 arcae = "^0.2.4"
 typing-extensions = { version = "^4.12.2", python = "<3.11" }
+zarr = {version = "^2.18.3", optional = true, extras = ["testing"]}
 
 [tool.poetry.extras]
 testing = ["dask", "distributed", "pytest"]