diff --git a/tox.ini b/tox.ini
index 758d681..69e9d57 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,11 +4,10 @@
 skipsdist = True
 
 [testenv]
-sitepackages = True
 setenv = VIRTUAL_ENV={envdir}
          OS_TEST_PATH=./tempest/test_discover
 usedevelop = True
-install_command = pip install {opts} {packages}
+install_command = pip install -U {opts} {packages}
 
 [testenv:py26]
 setenv = OS_TEST_PATH=./tempest/tests
@@ -27,11 +26,13 @@
 commands = python setup.py testr --coverage --testr-arg='tempest\.tests {posargs}'
 
 [testenv:all]
+sitepackages = True
 setenv = VIRTUAL_ENV={envdir}
 commands =
   python setup.py testr --slowest --testr-args='{posargs}'
 
 [testenv:full]
+sitepackages = True
 # The regex below is used to select which tests to run and exclude the slow tag:
 # See the testrepostiory bug: https://bugs.launchpad.net/testrepository/+bug/1208610
 commands =
@@ -44,24 +45,29 @@
   bash tools/pretty_tox_serial.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
 
 [testenv:testr-full]
+sitepackages = True
 commands =
   bash tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario|thirdparty|cli)) {posargs}'
 
 [testenv:heat-slow]
+sitepackages = True
 setenv = OS_TEST_TIMEOUT=1200
 # The regex below is used to select heat api/scenario tests tagged as slow.
 commands =
   bash tools/pretty_tox_serial.sh '(?=.*\[.*\bslow\b.*\])(^tempest\.(api|scenario)\.orchestration) {posargs}'
 
 [testenv:large-ops]
+sitepackages = True
 commands =
   python setup.py testr --slowest --testr-args='tempest.scenario.test_large_ops {posargs}'
 
 [testenv:smoke]
+sitepackages = True
 commands =
    bash tools/pretty_tox.sh '(?!.*\[.*\bslow\b.*\])((smoke)|(^tempest\.scenario)) {posargs}'
 
 [testenv:smoke-serial]
+sitepackages = True
 # This is still serial because neutron doesn't work with parallel. See:
 # https://bugs.launchpad.net/tempest/+bug/1216076 so the neutron smoke
 # job would fail if we moved it to parallel.
@@ -69,6 +75,7 @@
    bash tools/pretty_tox_serial.sh '(?!.*\[.*\bslow\b.*\])((smoke)|(^tempest\.scenario)) {posargs}'
 
 [testenv:stress]
+sitepackages = True
 commands =
     python -m tempest/stress/run_stress -a -d 3600 -S