diff --git a/manifests/magnum.pp b/manifests/magnum.pp
index 53c26795..9a999278 100644
--- a/manifests/magnum.pp
+++ b/manifests/magnum.pp
@@ -11,8 +11,9 @@
 #   Defaults to true
 #
 # [*image_source*]
-#   (Optional) If provision_image is true, the location of the image
-#   Defaults to 'https://fedorapeople.org/groups/magnum/fedora-atomic-latest.qcow2'
+#   (Optional) If provision_image is true, the location of the image. Required
+#   when provision_image is true
+#   Defaults to undef
 #
 # [*image_os_distro*]
 #   (Optional) If provision_image is true, the os_distro propery of the image
@@ -76,24 +77,24 @@
 #   Defaults to undef
 #
 class tempest::magnum (
-  Boolean $provision_image       = true,
-  String[1] $image_source        = 'https://fedorapeople.org/groups/magnum/fedora-atomic-latest.qcow2',
-  String[1] $image_name          = 'fedora-atomic-latest',
-  String[1] $image_os_distro     = 'fedora-atomic',
-  Boolean $provision_flavors     = true,
-  String[1] $flavor_id           = 's1.magnum',
-  String[1] $master_flavor_id    = 'm1.magnum',
-  Boolean $provision_keypair     = false,
-  $keypair_name                  = $facts['os_service_default'],
-  $nic_id                        = $facts['os_service_default'],
-  $magnum_url                    = $facts['os_service_default'],
-  $copy_logs                     = $facts['os_service_default'],
-  $dns_nameserver                = $facts['os_service_default'],
-  $catalog_type                  = $facts['os_service_default'],
-  Boolean $manage_tests_packages = true,
+  Boolean $provision_image          = true,
+  Optional[String[1]] $image_source = undef,
+  String[1] $image_name             = 'fedora-atomic-latest',
+  String[1] $image_os_distro        = 'fedora-atomic',
+  Boolean $provision_flavors        = true,
+  String[1] $flavor_id              = 's1.magnum',
+  String[1] $master_flavor_id       = 'm1.magnum',
+  Boolean $provision_keypair        = false,
+  $keypair_name                     = $facts['os_service_default'],
+  $nic_id                           = $facts['os_service_default'],
+  $magnum_url                       = $facts['os_service_default'],
+  $copy_logs                        = $facts['os_service_default'],
+  $dns_nameserver                   = $facts['os_service_default'],
+  $catalog_type                     = $facts['os_service_default'],
+  Boolean $manage_tests_packages    = true,
   # DEPRECATED PARAMETERS
-  $keypair_id                    = undef,
-  $tempest_config_file           = undef,
+  $keypair_id                       = undef,
+  $tempest_config_file              = undef,
 ) {
   include tempest::params
   include tempest
@@ -108,6 +109,10 @@ Use the keypair_name parameter.")
   }
 
   if $provision_image {
+    if $image_source == undef {
+      fail('The image_source parameter must be set when provision_image is true')
+    }
+
     $image_properties = { 'os_distro' => $image_os_distro }
     glance_image { $image_name:
       ensure           => present,
diff --git a/spec/classes/tempest_magnum_spec.rb b/spec/classes/tempest_magnum_spec.rb
index 2b390198..3b7e96e1 100644
--- a/spec/classes/tempest_magnum_spec.rb
+++ b/spec/classes/tempest_magnum_spec.rb
@@ -10,16 +10,19 @@ describe 'tempest::magnum' do
   end
 
   let :params do
-    { :nic_id => 'b2e6021a-4956-4a1f-8329-790b9add05a9', }
+    {
+      :image_source => 'https://fedorapeople.org/groups/magnum/fedora-atomic-latest.qcow2',
+      :nic_id       => 'b2e6021a-4956-4a1f-8329-790b9add05a9',
+    }
   end
 
   shared_examples 'tempest magnum' do
     context 'with default parameters' do
       it 'provisions resources and configures tempest for magnum' do
         is_expected.to contain_glance_image('fedora-atomic-latest').with(
-            :ensure     => 'present',
-            :source     => 'https://fedorapeople.org/groups/magnum/fedora-atomic-latest.qcow2',
-            :properties => '{"os_distro"=>"fedora-atomic"}'
+          :ensure     => 'present',
+          :source     => 'https://fedorapeople.org/groups/magnum/fedora-atomic-latest.qcow2',
+          :properties => {'os_distro' => 'fedora-atomic'}
         )
         is_expected.to contain_nova_flavor('s1.magnum').with_ensure('present')
         is_expected.to contain_nova_flavor('m1.magnum').with_ensure('present')
@@ -53,6 +56,10 @@ describe 'tempest::magnum' do
         })
       end
 
+      it 'should not provision the image' do
+        is_expected.to_not contain_glance_image('coreos')
+      end
+
       it 'configures tempest for magnum' do
         is_expected.to contain_tempest_config('magnum/image_id').with_value('coreos')
         is_expected.to contain_tempest_config('magnum/nic_id').with_value('b2e6021a-4956-4a1f-8329-790b9add05a9')