diff --git a/setup.py b/setup.py
index <HASH>..<HASH> 100755
--- a/setup.py
+++ b/setup.py
@@ -91,10 +91,10 @@ setup(
     'Programming Language :: Python :: 2',
     'Programming Language :: Python :: 2.7',
     'Programming Language :: Python :: 3',
-    'Programming Language :: Python :: 3.5',
     'Programming Language :: Python :: 3.6',
     'Programming Language :: Python :: 3.7',
     'Programming Language :: Python :: 3.8',
+    'Programming Language :: Python :: 3.9',
     'Programming Language :: Python :: Implementation :: CPython',
     'Topic :: Security',
     'Topic :: Software Development'
@@ -103,6 +103,7 @@ setup(
     'Source': 'https://github.com/secure-systems-lab/securesystemslib',
     'Issues': 'https://github.com/secure-systems-lab/securesystemslib/issues',
   },
+  python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, !=3.5.*, <4",
   install_requires = ['six>=1.11.0', 'subprocess32; python_version < "3"'],
   extras_require = {
       'colors': ['colorama>=0.3.9'],
Drop EOLed Python<I> and add stable <I> support

Python <I> has now reached its end-of-life and has been retired.
<URL> 'cryptography' dependency
has also just dropped support for <I>. Continuing support for <I>
does not seem worth the effort.

Instead we add support for the new stable Python <I>.