diff --git a/pyproject.toml b/pyproject.toml
index c464019..7122595 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,6 +19,7 @@ classifiers = [
     "Development Status :: 4 - Beta",
     "Programming Language :: Python",
     "Programming Language :: Python :: 3",
+    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
@@ -26,7 +27,7 @@ classifiers = [
     "Operating System :: OS Independent",
     "Topic :: Scientific/Engineering"
 ]
-requires-python = ">=3.10"
+requires-python = ">=3.9"
 dependencies = [
     "bw2parameters",
     "multifunctional>=0.4.3",