diff --git a/lib/micropub/models/post.rb b/lib/micropub/models/post.rb
index 22e41c7..ce0a0d1 100644
--- a/lib/micropub/models/post.rb
+++ b/lib/micropub/models/post.rb
@@ -34,7 +34,7 @@ class Post
   end
 
   def categories
-    params["category"]
+    params["category"] || []
   end
 
   def content