diff --git a/buildbot/slave/init.sls b/buildbot/slave/init.sls
index 23695539..9f012889 100644
--- a/buildbot/slave/init.sls
+++ b/buildbot/slave/init.sls
@@ -9,6 +9,7 @@ buildbot-slave-dependencies:
     - pkgs:
       - buildbot-slave == 0.8.12
       - twisted == 16.6.0 # NOTE: keep in sync with buildbot-master sls
+    - ignore_installed: True
     - require:
       - pkg: pip
 
diff --git a/python/init.sls b/python/init.sls
index f66c6787..11291dec 100644
--- a/python/init.sls
+++ b/python/init.sls
@@ -55,5 +55,6 @@ virtualenv:
   pip.installed:
     - pkgs:
       - virtualenv == 14.0.6
+    - ignore_installed: True
     - require:
       - pkg: pip
diff --git a/servo-build-dependencies/init.sls b/servo-build-dependencies/init.sls
index 9e2cefeb..c0522949 100644
--- a/servo-build-dependencies/init.sls
+++ b/servo-build-dependencies/init.sls
@@ -101,6 +101,7 @@ servo-dependencies:
     - require:
       - pkg: pip
       - pip: virtualenv
+    - ignore_installed: True
   {% endif %}
 
 {% if grains['os'] == 'Ubuntu' %}