diff --git a/lib/declarative/heritage.rb b/lib/declarative/heritage.rb
index <HASH>..<HASH> 100644
--- a/lib/declarative/heritage.rb
+++ b/lib/declarative/heritage.rb
@@ -1,3 +1,5 @@
+require "declarative/deep_dup"
+
 module Declarative
   class Heritage < Array
     # Record inheritable assignments for replay in an inheriting class.
diff --git a/lib/declarative/schema.rb b/lib/declarative/schema.rb
index <HASH>..<HASH> 100644
--- a/lib/declarative/schema.rb
+++ b/lib/declarative/schema.rb
@@ -1,6 +1,6 @@
-require "declarative"
 require "declarative/definitions"
 require "declarative/defaults"
+require "declarative/heritage"
 
 module Declarative
   # Include this to maintain inheritable, nested schemas with ::defaults and
Fix warning about circular require

```
declarative-<I>/lib/declarative.rb:5:
  warning: loading in progress, circular require considered harmful
```