diff --git a/data/helpers.d/utils b/data/helpers.d/utils
index 70643c64a..62d7b0c0b 100644
--- a/data/helpers.d/utils
+++ b/data/helpers.d/utils
@@ -393,7 +393,8 @@ ynh_replace_vars () {
     for one_var in "${uniques_vars[@]}"
     do
         # Validate that one_var is indeed defined
-        test -n "${!one_var:-}" || ynh_die --message="\$$one_var wasn't initialized when trying to replace __${one_var^^}__ in $file"
+        # Explanation for the weird '+x' syntax: https://stackoverflow.com/a/13864829
+        test -n "${one_var+x}" || ynh_die --message="Variable \$$one_var wasn't initialized when trying to replace __${one_var^^}__ in $file"
 
         # Escape delimiter in match/replace string
         match_string="__${one_var^^}__"