diff --git a/manifests/network.pp b/manifests/network.pp
index dc5ba06..1692704 100644
--- a/manifests/network.pp
+++ b/manifests/network.pp
@@ -1,33 +1,41 @@
 # @summary Creates network config for systemd-networkd
 define systemd::network (
   Enum['file', 'absent']         $ensure          = file,
   Stdlib::Absolutepath           $path            = '/etc/systemd/network',
   Optional[String]               $content         = undef,
   Optional[String]               $source          = undef,
   Optional[Stdlib::Absolutepath] $target          = undef,
   String                         $owner           = 'root',
   String                         $group           = 'root',
   String                         $mode            = '0444',
   Boolean                        $show_diff       = true,
   Boolean                        $restart_service = true,
 ) {
   include systemd
 
   if $restart_service and $systemd::manage_networkd {
     $notify = Service['systemd-networkd']
   } else {
     $notify = undef
   }
 
+  if $ensure == 'file' {
+    if $content =~ Undef and $source =~ Undef {
+      fail('Either content or source must be set')
+    }
+    if $content =~ NotUndef and $source =~ NotUndef {
+      fail('Either content or source must be set but not both')
+    }
+  }
   file { "${path}/${name}":
     ensure    => $ensure,
     content   => $content,
     source    => $source,
     target    => $target,
     owner     => $owner,
     group     => $group,
     mode      => $mode,
     show_diff => $show_diff,
     notify    => $notify,
   }
 }
diff --git a/spec/defines/network_spec.rb b/spec/defines/network_spec.rb
index 3ab5acc..dac8219 100644
--- a/spec/defines/network_spec.rb
+++ b/spec/defines/network_spec.rb
@@ -1,67 +1,84 @@
 require 'spec_helper'
 
 describe 'systemd::network' do
   context 'supported operating systems' do
     on_supported_os.each do |os, facts|
       context "on #{os}" do
         # manage systemd-networkd service
         let :pre_condition do
           "class { 'systemd':
             manage_networkd => true,
           }"
         end
 
         let(:facts) { facts }
 
         let(:title) { 'eth0.network' }
 
         let(:params) do
           {
             content: 'random stuff',
             restart_service: true,
           }
         end
 
         it { is_expected.to compile.with_all_deps }
 
         it {
           is_expected.to create_file("/etc/systemd/network/#{title}").with(
             ensure: 'file',
             content: %r{#{params[:content]}},
             mode: '0444'
           )
         }
 
         it { is_expected.to create_file("/etc/systemd/network/#{title}").that_notifies('Service[systemd-networkd]') }
 
         context 'with group => systemd-network, mode => 0640 and show_diff => false' do
           let(:title) { 'wg0.netdev' }
 
           let(:params) do
             {
               content: 'secret string',
               group: 'systemd-network',
               mode: '0640',
               show_diff: false,
               restart_service: true,
             }
           end
 
           it { is_expected.to compile.with_all_deps }
 
           it {
             is_expected.to create_file("/etc/systemd/network/#{title}").with(
               ensure: 'file',
               content: %r{#{params[:content]}},
               group: 'systemd-network',
               mode: '0640',
               show_diff: false
             )
           }
 
           it { is_expected.to create_file("/etc/systemd/network/#{title}").that_notifies('Service[systemd-networkd]') }
         end
+        context 'without content and without source' do
+          let :params do
+            {}
+          end
+
+          it { is_expected.to compile.and_raise_error(%r{Either content or source must be set}) }
+        end
+        context 'with content and source' do
+          let :params do
+            {
+              content: 'bla',
+              source: 'foo'
+            }
+          end
+
+          it { is_expected.to compile.and_raise_error(%r{Either content or source must be set but not both}) }
+        end
       end
     end
   end
 end