diff --git a/lib/ash/type/struct.ex b/lib/ash/type/struct.ex
index 54ccded9..c34ae3d8 100644
--- a/lib/ash/type/struct.ex
+++ b/lib/ash/type/struct.ex
@@ -11,8 +11,7 @@ defmodule Ash.Type.Struct do
   @constraints [
     instance_of: [
       type: :atom,
-      doc: "The module the struct should be an instance of",
-      default: false
+      doc: "The module the struct should be an instance of"
     ]
   ]