diff --git a/lib/puppet/functions/ssh/ipaddresses.rb b/lib/puppet/functions/ssh/ipaddresses.rb
new file mode 100644
index 0000000..466647a
--- /dev/null
+++ b/lib/puppet/functions/ssh/ipaddresses.rb
@@ -0,0 +1,40 @@
+# @summary Returns ip addresses of network interfaces (except lo) found by facter.
+# @api private
+#
+# Returns all ip addresses of network interfaces (except lo) found by facter.
+# Special network interfaces (e.g. docker0) can be excluded by an exclude list.
+Puppet::Functions.create_function(:'ssh::ipaddresses') do
+  dispatch :ipaddresses do
+    # @param excluded_interfaces An array of interface names to be excluded.
+    # @return The IP addresses found.
+    optional_param 'Array[String[1]]', :excluded_interfaces
+    return_type 'Array[Stdlib::IP::Address]'
+  end
+
+  def ipaddresses(excluded_interfaces = [])
+    facts = closure_scope['facts']
+
+    # always exclude loopback interface
+    excluded_interfaces += ['lo']
+
+    result = []
+    facts['networking']['interfaces'].each do |iface, data|
+      # skip excluded interfaces
+      next if excluded_interfaces.include?(iface)
+
+      %w[bindings bindings6].each do |binding_type|
+        next unless data.key?(binding_type)
+        data[binding_type].each do |binding|
+          next unless binding.key?('address')
+          result << binding['address']
+        end
+      end
+    end
+
+    # Throw away any v6 link-local addresses
+    fe8064 = IPAddr.new('fe80::/64')
+    result.delete_if { |ip| fe8064.include? IPAddr.new(ip) }
+
+    result.uniq
+  end
+end
diff --git a/lib/puppet/parser/functions/ipaddresses.rb b/lib/puppet/parser/functions/ipaddresses.rb
deleted file mode 100644
index 432871d..0000000
--- a/lib/puppet/parser/functions/ipaddresses.rb
+++ /dev/null
@@ -1,41 +0,0 @@
-module Puppet::Parser::Functions
-  newfunction(:ipaddresses, type: :rvalue, doc: <<-EOS
-  Returns all ip addresses of network interfaces (except lo) found by facter.
-  Special network interfaces (e.g. docker0) can be excluded by an exclude list as
-  first argument for this function.
-EOS
-             ) do |args|
-    networking = lookupvar('networking')
-
-    # always exclude loopback interface
-    interfaces_exclude = ['lo']
-    if args.size == 1
-      unless args[0].is_a?(Array)
-        raise(Puppet::ParseError, 'ipaddresses(): Requires first argument to be an Array')
-      end
-      interfaces_exclude << args[0]
-    end
-
-    return false unless networking.include?('interfaces')
-
-    result = []
-    networking['interfaces'].each do |iface, data|
-      # skip excluded interfaces
-      next if interfaces_exclude.include?(iface)
-
-      %w[bindings bindings6].each do |binding_type|
-        next unless data.key?(binding_type)
-        data[binding_type].each do |binding|
-          next unless binding.key?('address')
-          result << binding['address']
-        end
-      end
-    end
-
-    # Throw away any v6 link-local addresses
-    fe8064 = IPAddr.new('fe80::/64')
-    result.delete_if { |ip| fe8064.include? IPAddr.new(ip) }
-
-    return result.uniq
-  end
-end
diff --git a/manifests/hostkeys.pp b/manifests/hostkeys.pp
index f766281..5271681 100644
--- a/manifests/hostkeys.pp
+++ b/manifests/hostkeys.pp
@@ -1,45 +1,45 @@
 # Class ssh::hostkeys
 class ssh::hostkeys(
   Boolean          $export_ipaddresses  = true,
   Optional[String] $storeconfigs_group  = undef,
   Array            $extra_aliases       = [],
   Array            $exclude_interfaces  = [],
   Array            $exclude_ipaddresses = [],
 ) {
 
   if $export_ipaddresses == true {
-    $ipaddresses = ipaddresses($exclude_interfaces)
+    $ipaddresses = ssh::ipaddresses($exclude_interfaces)
     $ipaddresses_real = $ipaddresses - $exclude_ipaddresses
     $host_aliases = unique(flatten([ $::fqdn, $::hostname, $extra_aliases, $ipaddresses_real ]))
   } else {
     $host_aliases = unique(flatten([ $::fqdn, $::hostname, $extra_aliases]))
   }
 
   if $storeconfigs_group {
     tag 'hostkey_all', "hostkey_${storeconfigs_group}"
   }
 
   ['dsa', 'rsa', 'ecdsa', 'ed25519'].each |String $key_type| {
     # can be removed as soon as we drop support for puppet 4
     # see https://tickets.puppetlabs.com/browse/FACT-1377?jql=project%20%3D%20FACT%20AND%20fixVersion%20%3D%20%22FACT%203.12.0%22
     if $key_type == 'ecdsa' {
       $key_type_real = 'ecdsa-sha2-nistp256'
     } else {
       $key_type_real = $key_type
     }
 
     if $key_type in $facts['ssh'] {
       @@sshkey { "${::fqdn}_${key_type}":
         ensure       => present,
         host_aliases => $host_aliases,
         type         => $key_type_real,
         key          => $facts['ssh'][$key_type]['key'],
       }
     } else {
       @@sshkey { "${::fqdn}_${key_type}":
         ensure => absent,
         type   => $key_type_real,
       }
     }
   }
 }
diff --git a/metadata.json b/metadata.json
index 6475f3b..0c8331c 100644
--- a/metadata.json
+++ b/metadata.json
@@ -1,64 +1,64 @@
 {
   "name": "saz-ssh",
   "version": "5.0.0",
   "author": "saz",
   "summary": "Manage SSH client and server via Puppet.",
   "description": "Manage SSH client and server via puppet",
   "license": "Apache-2.0",
   "source": "git://github.com/saz/puppet-ssh.git",
   "project_page": "https://github.com/saz/puppet-ssh",
   "dependencies": [
     {
       "name": "puppetlabs/stdlib",
-      "version_requirement": ">= 4.24.0 < 7.0.0"
+      "version_requirement": ">= 4.25.0 < 7.0.0"
     },
     {
       "name": "puppetlabs/concat",
       "version_requirement": ">= 2.2.0 < 7.0.0"
     }
   ],
   "operatingsystem_support": [
     {
       "operatingsystem": "RedHat"
     },
     {
       "operatingsystem": "CentOS"
     },
     {
       "operatingsystem": "OracleLinux"
     },
     {
       "operatingsystem": "Scientific"
     },
     {
       "operatingsystem": "Debian"
     },
     {
       "operatingsystem": "Ubuntu"
     },
     {
       "operatingsystem": "FreeBSD"
     },
     {
       "operatingsystem": "DragonFly"
     },
     {
       "operatingsystem": "OpenBSD"
     },
     {
       "operatingsystem": "Gentoo"
     },
     {
       "operatingsystem": "Solaris"
     },
     {
       "operatingsystem": "ArchLinux"
     }
   ],
   "requirements": [
     {
       "name": "puppet",
       "version_requirement": ">= 4.10.10 < 7.0.0"
     }
   ]
 }
diff --git a/spec/fixtures/.gitignore b/spec/fixtures/.gitignore
index 0616a13..8182073 100644
--- a/spec/fixtures/.gitignore
+++ b/spec/fixtures/.gitignore
@@ -1,5 +1,6 @@
 # Ignore everything in this directory
 *
-# Except this file
+# Except these files
 !.gitignore
 !site.pp
+!mock-interface-fact.json
diff --git a/spec/fixtures/mock-interface-fact.json b/spec/fixtures/mock-interface-fact.json
new file mode 100644
index 0000000..b6ed4cc
--- /dev/null
+++ b/spec/fixtures/mock-interface-fact.json
@@ -0,0 +1,89 @@
+{
+  "networking": {
+    "interfaces": {
+      "docker0": {
+        "bindings": [
+          {
+            "address": "172.17.0.1",
+            "netmask": "255.255.0.0",
+            "network": "172.17.0.0"
+          }
+        ],
+        "bindings6": [
+          {
+            "address": "fe80::42:2fff:fea3:f2b7",
+            "netmask": "ffff:ffff:ffff:ffff::",
+            "network": "fe80::"
+          }
+        ],
+        "ip": "172.17.0.1",
+        "ip6": "fe80::42:2fff:fea3:f2b7",
+        "mac": "02:42:2f:a3:f2:b7",
+        "mtu": 1500,
+        "netmask": "255.255.0.0",
+        "netmask6": "ffff:ffff:ffff:ffff::",
+        "network": "172.17.0.0",
+        "network6": "fe80::"
+      },
+      "eno1": {
+        "bindings": [
+          {
+            "address": "10.13.42.61",
+            "netmask": "255.255.255.0",
+            "network": "10.13.42.0"
+          },
+          {
+            "address": "10.0.0.110",
+            "netmask": "255.255.255.255",
+            "network": "10.0.0.110"
+          },
+          {
+            "address": "10.0.0.104"
+          },
+          {
+            "address": "10.0.0.109"
+          }
+        ],
+        "bindings6": [
+          {
+            "address": "fe80::6544:473a:6ea4:c385",
+            "netmask": "ffff:ffff:ffff:ffff::",
+            "network": "fe80::"
+          }
+        ],
+        "dhcp": "10.13.42.1",
+        "ip": "10.13.42.61",
+        "ip6": "fe80::6544:473a:6ea4:c385",
+        "mac": "08:00:20:97:23:d1",
+        "mtu": 1500,
+        "netmask": "255.255.255.0",
+        "netmask6": "ffff:ffff:ffff:ffff::",
+        "network": "10.13.42.0",
+        "network6": "fe80::"
+      },
+      "lo": {
+        "bindings": [
+          {
+            "address": "127.0.0.1",
+            "netmask": "255.0.0.0",
+            "network": "127.0.0.0"
+          }
+        ],
+        "bindings6": [
+          {
+            "address": "::1",
+            "netmask": "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff",
+            "network": "::1"
+          }
+        ],
+        "ip": "127.0.0.1",
+        "ip6": "::1",
+        "mtu": 65536,
+        "netmask": "255.0.0.0",
+        "netmask6": "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff",
+        "network": "127.0.0.0",
+        "network6": "::1"
+      }
+    }
+  }
+}
diff --git a/spec/functions/ssh/ipaddresses_spec.rb b/spec/functions/ssh/ipaddresses_spec.rb
new file mode 100644
index 0000000..b968986
--- /dev/null
+++ b/spec/functions/ssh/ipaddresses_spec.rb
@@ -0,0 +1,30 @@
+require 'spec_helper'
+
+describe 'ssh::ipaddresses', type: :puppet_function do
+  it 'exists' do
+    is_expected.not_to be_nil
+  end
+
+  context 'with dummy fact data' do
+    let(:facts) do
+      JSON.parse File.read(File.join(File.dirname(__FILE__), '../../fixtures/mock-interface-fact.json'))
+    end
+
+    describe 'without parameters' do
+      it 'returns all IPs other than localhost' do
+        is_expected.to run.and_return(['172.17.0.1', '10.13.42.61', '10.0.0.110', '10.0.0.104', '10.0.0.109'])
+      end
+    end
+
+    describe 'with excluded interface' do
+      it 'doesn\'t return the IPs of excluded interface' do
+        is_expected.to run.with_params(['docker0']).and_return(['10.13.42.61', '10.0.0.110', '10.0.0.104', '10.0.0.109'])
+      end
+    end
+    describe 'with excluded interfaces' do
+      it 'doesn\'t return the IPs of those interfaces' do
+        is_expected.to run.with_params(%w[docker0 eno1]).and_return([])
+      end
+    end
+  end
+end