diff --git a/pyproject.toml b/pyproject.toml
index b164558..1c160c2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -16,6 +16,7 @@ classifiers = [
     "Operating System :: Unix",
     "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
+    "Programming Language :: Python :: 3 :: Only",
     "Topic :: Utilities",
 ]