diff --git a/.circleci/setup-virtualenv.sh b/.circleci/setup-virtualenv.sh
index 5e8668126..600647672 100755
--- a/.circleci/setup-virtualenv.sh
+++ b/.circleci/setup-virtualenv.sh
@@ -14,7 +14,7 @@ sudo --set-home -u nobody virtualenv --python python2.7 /tmp/tests
 # installed.  SSL support in setuptools is needed in case packages use
 # `setup_requires` which gets satisfied by setuptools instead of by pip.
 # txi2p (vcversioner) is one such package.  Twisted (incremental) is another.
-sudo --set-home -u nobody /tmp/tests/bin/pip install certifi tox codecov
+sudo --set-home -u nobody /tmp/tests/bin/pip install tox codecov
 
 # Get everything else installed in it, too.
 sudo --set-home -u nobody /tmp/tests/bin/tox -c /tmp/project/tox.ini --workdir /tmp --notest -e "${TAHOE_LAFS_TOX_ENVIRONMENT}" ${TAHOE_LAFS_TOX_ARGS}
diff --git a/tox.ini b/tox.ini
index d27cd0637..25061754a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,12 +14,13 @@ skipsdist = True
 [testenv]
 basepython=python2.7
 passenv = TAHOE_LAFS_* USERPROFILE HOMEDRIVE HOMEPATH
-# Pre-install "incremental" to avoid bug #2913. Basically if Twisted's
-# setup_requires=["incremental"] causes this to be installed (with
-# setuptools), then it'll fail on travis's OS-X 10.12 machines when PyPI
-# disables access with TLS-1.1 or older, so we have to install it ahead of
-# time (with pip).
-deps = incremental
+# Get "certifi" to avoid bug #2913. Basically if a `setup_requires=...` causes
+# a package to be installed (with setuptools) then it'll fail on certain
+# platforms (travis's OX-X 10.12, Slackware 14.2) because PyPI's TLS
+# requirements (TLS >= 1.2) are incompatible with the old TLS clients
+# available to those systems.  Installing it ahead of time (with pip) avoids
+# this problem.
+deps = certifi
 # We add usedevelop=True for speed, and extras=test to get things like "mock"
 # that are required for our unit tests.
 usedevelop = True