diff --git a/spec-0004/index.md b/spec-0004/index.md
index d50b0880..5994dcf8 100644
--- a/spec-0004/index.md
+++ b/spec-0004/index.md
@@ -21,6 +21,7 @@ endorsed-by:
   - scikit-learn
   - scipy
   - xarray
+  - zarr
 ---
 
 ## Description