diff --git a/pyproject.toml b/pyproject.toml
index 56536ec..cd649ef 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,7 +19,7 @@ classifiers = [
 description-file="README.md"
 requires = [
     "jinja2",
-    "ruamel_yaml<0.18",
+    "ruamel_yaml<0.18", # the code is not compatible with ruamel 0.18
     "matplotlib",
     "pandas",
     "pygments",