1 files changed, 1 insertions, 6 deletions
diff --git a/tox.ini b/tox.ini
index 6dcc439a40..c232676826 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = packaging, py35, py36, py37, py38, check_codestyle, check_isort
+envlist = packaging, py35, py36, py37, py38, py39, check_codestyle, check_isort
 
 [base]
 extras = test
@@ -24,11 +24,6 @@ deps =
     pip>=10
 
 setenv =
-    # we have a pyproject.toml, but don't want pip to use it for building.
-    # (otherwise we get an error about 'editable mode is not supported for
-    # pyproject.toml-style projects').
-    PIP_USE_PEP517 = false
-
     PYTHONDONTWRITEBYTECODE = no_byte_code
     COVERAGE_PROCESS_START = {toxinidir}/.coveragerc