diff --git a/.github/workflows/test-ci.yml b/.github/workflows/test-ci.yml
index 701b4fd2..ec6f3791 100644
--- a/.github/workflows/test-ci.yml
+++ b/.github/workflows/test-ci.yml
@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.5, 3.6, 3.7, 3.8, 3.9]
     runs-on: ${{ matrix.os }}
 
     steps:
diff --git a/run_tests b/run_tests
index 07cd98db..6c6f8594 100755
--- a/run_tests
+++ b/run_tests
@@ -34,8 +34,8 @@ def find_pytest():
   if ret:
     return ret
 
-  print(f'{__file__}: unable to find pytest.', file=sys.stderr)
-  print(f'{__file__}: Try installing: sudo apt-get install python-pytest',
+  print('%s: unable to find pytest.' % (__file__,), file=sys.stderr)
+  print('%s: Try installing: sudo apt-get install python-pytest' % (__file__,),
         file=sys.stderr)
 
 
diff --git a/setup.py b/setup.py
index 17aeae22..9d0ff5f9 100755
--- a/setup.py
+++ b/setup.py
@@ -56,6 +56,6 @@ setuptools.setup(
         'Programming Language :: Python :: 3 :: Only',
         'Topic :: Software Development :: Version Control :: Git',
     ],
-    python_requires='>=3.6',
+    python_requires='>=3.5',
     packages=['subcmds'],
 )
diff --git a/tox.ini b/tox.ini
index b4758d1d..3282de14 100644
--- a/tox.ini
+++ b/tox.ini
@@ -15,13 +15,15 @@
 # https://tox.readthedocs.io/
 
 [tox]
-envlist = py36, py37, py38
+envlist = py35, py36, py37, py38, py39
 
 [gh-actions]
 python =
+    3.5: py35
     3.6: py36
     3.7: py37
     3.8: py38
+    3.9: py39
 
 [testenv]
 deps = pytest