diff --git a/lib.nix b/lib.nix
index 9e05c84..12712b1 100644
--- a/lib.nix
+++ b/lib.nix
@@ -128,7 +128,7 @@ in
           echo
           echo "PostgreSQL is setting up the initial database"
           echo
-          if [[ -z "$PGHOST" ]]; then
+          if [[ -z "$\{PGHOST+x}" ]]; then
             OLDPGHOST=""
           else
             OLDPGHOST="$PGHOST"