diff --git a/lib/puppet/provider/zfs/zfs.rb b/lib/puppet/provider/zfs/zfs.rb
index 57d0b36..7a2f5df 100644
--- a/lib/puppet/provider/zfs/zfs.rb
+++ b/lib/puppet/provider/zfs/zfs.rb
@@ -1,104 +1,104 @@
 Puppet::Type.type(:zfs).provide(:zfs) do
   desc 'Provider for zfs.'
 
   commands zfs: 'zfs'
 
   def self.instances
     zfs(:list, '-H').split("\n").map do |line|
       name, _used, _avail, _refer, _mountpoint = line.split(%r{\s+})
       new(name: name, ensure: :present)
     end
   end
 
   def add_properties
     properties = []
     Puppet::Type.type(:zfs).validproperties.each do |property|
       next if property == :ensure
       if (value = @resource[property]) && value != ''
         if property == :volsize
           properties << '-V' << value.to_s
         else
           properties << '-o' << "#{property}=#{value}"
         end
       end
     end
     properties
   end
 
   def create
     zfs(*([:create] + add_properties + [@resource[:name]]))
   end
 
   def destroy
     zfs(:destroy, @resource[:name])
   end
 
   def exists?
     zfs(:list, @resource[:name])
     true
   rescue Puppet::ExecutionFailure
     false
   end
 
   # On FreeBSD zoned is called jailed
   def container_property
     case Facter.value(:operatingsystem)
     when 'FreeBSD'
       :jailed
     else
       :zoned
     end
   end
 
-  PARAMETER_UNSET_OR_NOT_AVAILABLE = '-'.freeze
+  PARAMETER_UNSET_OR_NOT_AVAILABLE = '-'.freeze unless defined? PARAMETER_UNSET_OR_NOT_AVAILABLE
 
   # https://docs.oracle.com/cd/E19963-01/html/821-1448/gbscy.html
   # shareiscsi (added in build 120) was removed from S11 build 136
   # aclmode was removed from S11 in build 139 but it may have been added back
   # acltype is for ZFS on Linux, and allows disabling or enabling POSIX ACLs
   # http://webcache.googleusercontent.com/search?q=cache:-p74K0DVsdwJ:developers.slashdot.org/story/11/11/09/2343258/solaris-11-released+&cd=13
   [:aclmode, :acltype, :shareiscsi, :overlay].each do |field|
     # The zfs commands use the property value '-' to indicate that the
     # property is not set. We make use of this value to indicate that the
     # property is not set since it is not available. Conversely, if these
     # properties are attempted to be unset, and resulted in an error, our
     # best bet is to catch the exception and continue.
     define_method(field) do
       begin
         zfs(:get, '-H', '-o', 'value', field, @resource[:name]).strip
       rescue
         PARAMETER_UNSET_OR_NOT_AVAILABLE
       end
     end
     define_method(field.to_s + '=') do |should|
       begin
         zfs(:set, "#{field}=#{should}", @resource[:name])
       rescue
         PARAMETER_UNSET_OR_NOT_AVAILABLE
       end
     end
   end
 
   [:aclinherit, :atime, :canmount, :checksum,
    :compression, :copies, :dedup, :devices, :exec, :logbias,
    :mountpoint, :nbmand, :primarycache, :quota, :readonly,
    :recordsize, :refquota, :refreservation, :reservation,
    :secondarycache, :setuid, :sharenfs, :sharesmb,
    :snapdir, :version, :volsize, :vscan, :xattr].each do |field|
     define_method(field) do
       zfs(:get, '-H', '-o', 'value', field, @resource[:name]).strip
     end
 
     define_method(field.to_s + '=') do |should|
       zfs(:set, "#{field}=#{should}", @resource[:name])
     end
   end
 
   define_method(:zoned) do
     zfs(:get, '-H', '-o', 'value', container_property, @resource[:name]).strip
   end
 
   define_method('zoned=') do |should|
     zfs(:set, "#{container_property}=#{should}", @resource[:name])
   end
 end