diff --git a/pkgs/development/compilers/rust/setup-hook.sh b/pkgs/development/compilers/rust/setup-hook.sh
index 7078ec7060b..5d4eb642fec 100644
--- a/pkgs/development/compilers/rust/setup-hook.sh
+++ b/pkgs/development/compilers/rust/setup-hook.sh
@@ -1,4 +1,4 @@
 # Fix 'failed to open: /homeless-shelter/.cargo/.package-cache' in rust 1.36.
-if [[ -z $IN_NIX_SHELL && -z $CARGO_HOME ]]; then
+if [[ -z ${IN_NIX_SHELL-} && -z ${CARGO_HOME-} ]]; then
     export CARGO_HOME=$TMPDIR
 fi