diff --git a/appveyor.yml b/appveyor.yml
index 0f0d65e492..c0fc296386 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -24,6 +24,7 @@ install:
   - python -m pip install -U pip setuptools
   - pip install -e .
   - pip install securesystemslib[crypto,pynacl]
+  - if %PYTHON_VERSION%==2.7 pip install mock
 
 build: false