diff --git a/lib/puppet/type/docker_compose.rb b/lib/puppet/type/docker_compose.rb
index c5f50851..718b1616 100644
--- a/lib/puppet/type/docker_compose.rb
+++ b/lib/puppet/type/docker_compose.rb
@@ -28,7 +28,7 @@ def refresh
   newparam(:up_args) do
     desc 'Arguments to be passed directly to docker-compose up.'
     validate do |value|
-      raise _('up_args should be a String') unless value.is_a? String
+      raise _('up_args should be a String') unless value.is_a? Array
     end
   end