diff --git a/lib.nix b/lib.nix
index e643a32..8cce73b 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+x}" ]]; then
+          if [[ -z "''${PGHOST+x}" ]]; then
             OLDPGHOST=""
           else
             OLDPGHOST="$PGHOST"