diff --git a/scripts/install-multi-user.sh b/scripts/install-multi-user.sh
index b4eec2fe9..6ee8dd485 100644
--- a/scripts/install-multi-user.sh
+++ b/scripts/install-multi-user.sh
@@ -727,7 +727,7 @@ setup_default_profile() {
     _sudo "to installing a bootstrapping Nix in to the default Profile" \
           HOME="$ROOT_HOME" "$NIX_INSTALLED_NIX/bin/nix-env" -i "$NIX_INSTALLED_NIX"
 
-    if [ -z "$NIX_SSL_CERT_FILE" ] || ! [ -f "$NIX_SSL_CERT_FILE" ]; then
+    if [ -z "${NIX_SSL_CERT_FILE:-}" ] || ! [ -f "${NIX_SSL_CERT_FILE:-}" ]; then
         _sudo "to installing a bootstrapping SSL certificate just for Nix in to the default Profile" \
               HOME="$ROOT_HOME" "$NIX_INSTALLED_NIX/bin/nix-env" -i "$NIX_INSTALLED_CACERT"
         export NIX_SSL_CERT_FILE=/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt