diff --git a/pkgs/by-name/jj/jj-pre-push/package.nix b/pkgs/by-name/jj/jj-pre-push/package.nix
index 827117002602..10856878706a 100644
--- a/pkgs/by-name/jj/jj-pre-push/package.nix
+++ b/pkgs/by-name/jj/jj-pre-push/package.nix
@@ -40,6 +40,9 @@ python3Packages.buildPythonApplication (finalAttrs: {
   nativeBuildInputs = [ installShellFiles ];
 
   postInstall = lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
+    # Generate completions for the requested shell instead of detecting the build shell.
+    export _TYPER_COMPLETE_TEST_DISABLE_SHELL_DETECTION=1
+
     installShellCompletion --cmd jj-pre-push \
       --bash <($out/bin/jj-pre-push --show-completion bash) \
       --fish <($out/bin/jj-pre-push --show-completion fish) \