diff --git a/.appveyor.yml b/.appveyor.yml
index 272198a29..d276b042e 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -18,7 +18,7 @@ environment:
 install:
   - python -m pip install -U pip setuptools wheel
   - pip install codecov
-  - pip install -U tox
+  - pip install tox==3.4.0
 build_script:
   - python setup.py bdist_wheel
 test_script:
diff --git a/.travis.yml b/.travis.yml
index 18e656c06..103b70681 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -39,7 +39,7 @@ matrix:
       python: "2.7"
 
 install:
-  - pip install tox-travis
+  - pip install tox==3.4.0 tox-travis
   - pip install codecov
   - pip install -U pip setuptools
   - python setup.py bdist_wheel