diff --git a/pyproject.toml b/pyproject.toml
index 1b7a5be8..f75ab512 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -110,7 +110,8 @@ dependencies = [ # Optional
   "xarray",
   "mpi4py",
   "icesat2-toolkit==1.0.0.22",
-  "geopandas"
+  "geopandas",
+  "sliderule"
 ]
 
 # List additional groups of dependencies   here (e.g. development