diff --git a/package.nix b/package.nix
index 403ff76..b76561f 100644
--- a/package.nix
+++ b/package.nix
@@ -4,6 +4,7 @@
 , nodejs_22
 , cacert
 , makeWrapper
+, installShellFiles
 , gnutar
 , gzip
 , openssl
@@ -102,7 +103,8 @@ stdenv.mkDerivation rec {
   dontPatchELF = runtime == "native";
   dontStrip = runtime == "native";
 
-  nativeBuildInputs = selected.nativeBuildInputs;
+  nativeBuildInputs = selected.nativeBuildInputs
+    ++ lib.optionals (selected.binName == "codex") [ installShellFiles ];
   buildInputs = selected.buildInputs;
 
   buildPhase = if runtime == "native" then ''
@@ -158,6 +160,13 @@ stdenv.mkDerivation rec {
     runHook postInstall
   '';
 
+  postInstall = lib.optionalString (selected.binName == "codex") ''
+    installShellCompletion --cmd codex \
+      --bash <("$out/bin/${selected.binName}" completion bash) \
+      --fish <("$out/bin/${selected.binName}" completion fish) \
+      --zsh <("$out/bin/${selected.binName}" completion zsh)
+  '';
+
   meta = with lib; {
     description = selected.description;
     homepage = "https://github.com/openai/codex";