diff --git a/lib/autoproj/package_set.rb b/lib/autoproj/package_set.rb
index a2884d6f..6bd8347d 100644
--- a/lib/autoproj/package_set.rb
+++ b/lib/autoproj/package_set.rb
@@ -421,7 +421,8 @@ def self.raw_description_file(raw_local_dir, package_set_name: nil)
                 source_definition.merge!(newdefs) do |k, old, new|
                     if old.respond_to?(:to_ary)
                         old + new
-                    else new
+                    else
+                        new
                     end
                 end
             end