diff --git a/py39.patch b/py39.patch
new file mode 100644
index 0000000..4e3c0d5
--- /dev/null
+++ b/py39.patch
@@ -0,0 +1,13 @@
+diff --git a/src/tox/constants.py b/src/tox/constants.py
+index bd21562..e1b7c3f 100644
+--- a/src/tox/constants.py
++++ b/src/tox/constants.py
+@@ -28,7 +28,7 @@ def _construct_default_factors(cpython_versions, pypy_versions, other_interprete
+ class PYTHON:
+     PY_FACTORS_RE = re.compile("^(?!py$)(py|pypy|jython)([2-9][0-9]?)?$")
+     PY_FACTORS_MAP = {"py": "python", "pypy": "pypy", "jython": "jython"}
+-    CPYTHON_VERSION_TUPLES = [(2, 7), (3, 4), (3, 5), (3, 6), (3, 7), (3, 8)]
++    CPYTHON_VERSION_TUPLES = [(2, 7), (3, 4), (3, 5), (3, 6), (3, 7), (3, 8), (3, 9)]
+     PYPY_VERSION_TUPLES = [(2, 7), (3, 5)]
+     OTHER_PYTHON_INTERPRETERS = ["jython"]
+     DEFAULT_FACTORS = _construct_default_factors(
diff --git a/python-tox.spec b/python-tox.spec
index 162ca55..572991b 100644
--- a/python-tox.spec
+++ b/python-tox.spec
@@ -7,13 +7,18 @@
 %global pypiname tox
 Name:           python-%{pypiname}
 Version:        3.5.3
-Release:        3%{?dist}
+Release:        4%{?dist}
 Summary:        Virtualenv-based automation of test activities
 
 # file toxbootstrap.py is licensed under MIT License
 License:        GPLv2+ and MIT
 URL:            http://tox.testrun.org/
 Source0:        https://files.pythonhosted.org/packages/source/t/%{pypiname}/%{pypiname}-%{version}.tar.gz
+
+# Run py39 env with Python 3.9
+# https://bugzilla.redhat.com/show_bug.cgi?id=1798929
+Patch1:         py39.patch
+
 BuildArch:      noarch
 
 %description
@@ -50,6 +55,7 @@ Recommends:     python35
 Recommends:     python36
 Recommends:     python37
 Recommends:     python38
+Recommends:     python39
 Recommends:     pypy-devel
 Recommends:     pypy3-devel
 Recommends:     python2-devel
@@ -62,6 +68,8 @@ Obsoletes:      python2-tox < 2.9.1-4
 # for tests
 BuildRequires:  python3-py
 BuildRequires:  python3-pytest
+BuildRequires:  python3-pytest-mock
+BuildRequires:  python3-pytest-xdist
 BuildRequires:  python3-virtualenv
 %endif
 
@@ -79,7 +87,7 @@ can use for:
    boilerplate and merging CI and shell-based testing.
 
 %prep
-%setup -q -n %{pypiname}-%{version}
+%autosetup -p1 -n %{pypiname}-%{version}
 
 # remove bundled egg-info
 rm -rf %{pypiname}.egg-info
@@ -94,7 +102,26 @@ rm -rf %{pypiname}.egg-info
 # if internet connection available, run tests
 %if %{with internet}
 %check
-TOXENV=py%{python3_version_nodots} %{__python3} setup.py test
+# there will be failures like
+#    ModuleNotFoundError: tox
+# or InterpreterNotFound: python
+# We juggle the environment variables as much as we can, but it's not perfect.
+# To workaround this:
+#    1. build --without internet
+#    2. install the new python3-tox
+#    3. build --with internet
+mkdir .path
+ln -s %{__python3} .path/python
+ln -s /usr/bin/easy_install-%{python3_version} .path/easy_install
+ln -s /usr/bin/pytest-%{python3_version} .path/pytest
+ln -s /usr/bin/pip3 .path/pip
+export PATH=$(pwd)/.path:%{buildroot}%{_bindir}:$PATH
+export PYTHONPATH=%{buildroot}%{python3_sitelib}
+export TOXENV=py%{python3_version_nodots}
+export TOX_TESTENV_PASSENV="PATH TOX_TESTENV_PASSENV"
+# TODO figure out why PEP517/518 tests and test_provision_cli_args_ignore won't pass
+pytest-3 -n auto -k "not test_verbose_isolated_build and not test_dist_exists_version_change and not test_alwayscopy"
+rm -rf .path
 %endif
 
 %files -n python3-%{pypiname}
@@ -104,6 +131,10 @@ TOXENV=py%{python3_version_nodots} %{__python3} setup.py test
 %{python3_sitelib}/%{pypiname}-%{version}-py%{python3_version}.egg-info
 
 %changelog
+* Thu Feb 06 2020 Miro Hrončok <mhroncok@redhat.com> - 3.5.3-4
+- Fix invocation with Python 3.9 (#1798929)
+- Recommend Python 3.9
+
 * Fri Feb 15 2019 Lumír Balhar <lbalhar@redhat.com> - 3.5.3-3
 - Recommend Python 3.8
 
diff --git a/tests/tests.yml b/tests/tests.yml
index 2f55b4f..6f66a50 100644
--- a/tests/tests.yml
+++ b/tests/tests.yml
@@ -26,14 +26,19 @@
     - smoke38:
         dir: python/smoke
         run: VERSION=3.8 ./venv.sh
+    - smoke39:
+        dir: python/smoke
+        run: VERSION=3.9 ./venv.sh
     required_packages:
     - gcc
-    - /usr/bin/virtualenv
+    - virtualenv
     - python27
     - python34
     - python35
     - python36
     - python37
+    - python38
+    - python39
     - python2-devel
     - python3-devel
     - python3-tox