diff --git a/pyproject.toml b/pyproject.toml
index e710bf9..f1c993a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -13,6 +13,7 @@ classifiers = [
 ]
 dependencies = [
     'astropy >=5.0.4',
+    'ullyses >= 3.0.0',
 ]
 dynamic = ['version']