diff --git a/quirks.nix b/quirks.nix
index 5c407aa..fb34a1f 100644
--- a/quirks.nix
+++ b/quirks.nix
@@ -26,12 +26,12 @@
     else
         PREFIX="Hint:"
     fi
-    if [ "$GITHUB_ACTIONS" = "true" ] || [ -v CODESPACE_TOKEN ]; then
+    if [ "$GITHUB_ACTIONS" = "true" ] || [ "$'' + ''{CODESPACE_TOKEN+x}" = "x" ]; then
         echo "$PREFIX to reproduce this environment locally, use either:" \
              "\`nix develop github:input-output-hk/devx#${flavor}\`, or" \
              "\`docker run -it -v \$(pwd):/workspaces ghcr.io/input-output-hk/devx-devcontainer:x86_64-linux.${flavor}\`"
     fi
-    if [ -v CODESPACE_TOKEN ]; then
+    if [ "$'' + ''{CODESPACE_TOKEN+x}" = "x" ]; then
         echo "Quirks:"
         echo -e "\tThe Haskell VSCode extension might ask you \"How do you want the extension to manage/discover HLS and the relevant toolchain?\""
         echo -e "\tChoose \"Manually via PATH\", not \"Automatically via GHCup\""