diff --git a/templates/pip.conf.j2 b/templates/pip.conf.j2
index 9b94138..07dd9c0 100644
--- a/templates/pip.conf.j2
+++ b/templates/pip.conf.j2
@@ -13,9 +13,9 @@ trusted-host =
 {% endif %}
 
 [install]
-upgrade = {{ pip_upgrade }}
+upgrade = {{ (pip_upgrade | bool) | lower }}
 upgrade-strategy = {{ pip_upgrade_strategy }}
-pre = {{ pip_enable_pre_releases }}
+pre = {{ (pip_enable_pre_releases | bool) | lower }}
 {% if pip_links | length > 0 %}
 find-links =
 {%   for pip_link in pip_links %}