diff --git a/pyproject.toml b/pyproject.toml
index 88ecb16f..b7e0b4d3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -36,7 +36,8 @@ optional = [
     "scipy",
     "shapely",
     "jinja2",  # for to_latex options
-    "pypestutils"
+    "pypestutils",
+    "scikit-learn",
 ]
 test = [
     "coveralls",