diff --git a/stage0/.claude/skills/port-astgen/SKILL.md b/stage0/.claude/skills/port-astgen/SKILL.md
index 3fd6c69638..aaf22fdd97 100644
--- a/stage0/.claude/skills/port-astgen/SKILL.md
+++ b/stage0/.claude/skills/port-astgen/SKILL.md
@@ -124,3 +124,6 @@ Go back to Step 1.
   Zig one, which is the source of the bug. So standard "bug hunting" methods no
   longer apply -- making implementations consistent is a much better approach
   in all ways.
+- From `zig build` commands, use *only* `zig build *-zig0`. Other `zig build`
+  commands may start building/testing zig itself, which takes ages and is
+  wholly unnecessary.