diff --git a/lib/alchemy.rb b/lib/alchemy.rb
index 45a27d26d0..a506b2161c 100644
--- a/lib/alchemy.rb
+++ b/lib/alchemy.rb
@@ -57,6 +57,10 @@ def self.preview_sources
     @_preview_sources ||= Set.new << Alchemy::Admin::PreviewUrl
   end
 
+  def self.preview_sources=(sources)
+    @_preview_sources = Array(sources)
+  end
+
   # Define page publish targets
   #
   # A publish target is a ActiveJob that gets performed