diff --git a/CLAUDE.md b/CLAUDE.md
index 8693868..f01c2c4 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -14,13 +14,13 @@ This repo uses Gitea (git.rev.iq) with the `tea` CLI for pull requests:
 - tea 0.10.1 is pinned in `nix/tea.nix` (0.11.x has TTY bugs)
 - Always specify `-r igm/publisher-dashboard` flag (SSH remote auto-detection doesn't work)
 
-## macOS sed Syntax
+## sed Syntax (GNU coreutils)
 
-macOS uses BSD sed which differs from GNU sed:
-- In-place edit requires empty string for backup: `sed -i '' 's/old/new/g' file`
-- GNU sed (Linux): `sed -i 's/old/new/g' file`
-- Use `|` as delimiter when patterns contain `/`: `sed -i '' 's|old/path|new/path|g' file`
-- For multiple files: `for f in *.txt; do sed -i '' 's/old/new/g' "$f"; done`
+This project uses GNU coreutils via devenv, so use standard GNU sed syntax:
+- In-place edit: `sed -i 's/old/new/g' file`
+- Use `|` as delimiter when patterns contain `/`: `sed -i 's|old/path|new/path|g' file`
+- For multiple files: `for f in *.txt; do sed -i 's/old/new/g' "$f"; done`
+- Do NOT use BSD sed syntax (`sed -i ''`) - we have GNU sed available
 
 ## SvelteKit resolve() Usage
 
diff --git a/devenv.nix b/devenv.nix
index 9aa07d1..0f0cc77 100644
--- a/devenv.nix
+++ b/devenv.nix
@@ -14,6 +14,7 @@ in
     dbmate
     ast-grep
     dbip-city-lite
+    gnused # GNU sed for consistent cross-platform behavior
   ];
 
   dotenv.enable = true;