diff --git a/setup.py b/setup.py
index e1ce14a..382f8f2 100644
--- a/setup.py
+++ b/setup.py
@@ -26,7 +26,8 @@ install_requires = [
 install_extras = {
     'client': [
         'gevent>=1.3.0',
-        'protobuf>=3.0.0,<3.18.0',
+        'protobuf>~3.0; python_version >= "3"',
+        'protobuf<3.18.0; python_version < "3"',
         'gevent-eventemitter~=2.1',
     ],
 }