diff --git a/pkgs/by-name/fl/fluxcd/package.nix b/pkgs/by-name/fl/fluxcd/package.nix
index 712f075459b6..8d691f58b5a5 100644
--- a/pkgs/by-name/fl/fluxcd/package.nix
+++ b/pkgs/by-name/fl/fluxcd/package.nix
@@ -60,8 +60,8 @@ buildGoModule rec {
 
   postInstall = lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
     for shell in bash fish zsh; do
-      $out/bin/flux completion $shell > flux.$shell
-      installShellCompletion flux.$shell
+      installShellCompletion --cmd flux \
+        --$shell <($out/bin/flux completion $shell)
     done
   '';