diff --git a/pyproject.toml b/pyproject.toml
index 9b884410..3df20cab 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,6 +17,9 @@ classifiers = [
     "Topic :: Software Development :: Testing",
     "Topic :: Software Development :: Quality Assurance",
     "Topic :: Software Development :: Libraries :: Python Modules",
+    "Operating System :: MacOS",
+    "Operating System :: POSIX :: Linux",
+    "Operating System :: Microsoft :: Windows",
     "Programming Language :: Python :: 2.7",
     "Programming Language :: Python :: 3.5",
     "Programming Language :: Python :: 3.6",