diff --git a/setup.cfg b/setup.cfg
index 09d0d48..7460814 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -15,6 +15,8 @@ classifier =
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3 :: Only
+    Programming Language :: Python :: Implementation :: CPython
     Topic :: Software Development :: Libraries
 
 [files]
diff --git a/tox.ini b/tox.ini
index 3f93d90..cd8e8a4 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,7 @@
 [tox]
 minversion = 3.1.1
 envlist = py37,docs,pep8
-ignore_basepython_conflict = True
+ignore_basepython_conflict = true
 
 [testenv]
 basepython = python3