diff --git a/prompts/CODE_STYLEGUIDE_GO.md b/prompts/CODE_STYLEGUIDE_GO.md
index f859589..4cc8e93 100644
--- a/prompts/CODE_STYLEGUIDE_GO.md
+++ b/prompts/CODE_STYLEGUIDE_GO.md
@@ -227,6 +227,14 @@ last_modified: 2026-02-22
      }
     ```
 
+1.  Do not create packages just to hold types (e.g. `types`, `domain`,
+    `models` that contain only type definitions). Define types alongside the
+    implementations that use them. A type-only package is a sign that the types
+    are in the wrong place — move them to the package that actually operates on
+    them. This also avoids awkward import aliases (e.g.
+    `domaintypes "myapp/internal/domain"`) which are a code smell indicating
+    poor package naming.
+
 1.  Define your struct types near their constructors.
 
 1.  Define your interface types near the functions that use them, or if you have