diff --git a/lib/puppet/type/glance_image.rb b/lib/puppet/type/glance_image.rb
index d63590d9..c4a85212 100644
--- a/lib/puppet/type/glance_image.rb
+++ b/lib/puppet/type/glance_image.rb
@@ -46,7 +46,8 @@ Puppet::Type.newtype(:glance_image) do
     newvalues(/(y|Y)es/, /(n|N)o/)
     defaultto('Yes')
     munge do |v|
-      v.to_s.capitalize
+      'True'  if v =~ /^(y|Y)es$/
+      'False' if v =~ /^(n|N)o$/
     end
   end