diff --git a/helpers/ruby b/helpers/ruby
index cc7c73f90..82a946935 100644
--- a/helpers/ruby
+++ b/helpers/ruby
@@ -9,7 +9,7 @@ export rbenv_root="$rbenv_install_dir"
 
 if dpkg --compare-versions ${YNH_APP_PACKAGING_FORMAT:-0} lt 2; then
 	build_ruby_dependencies="libjemalloc-dev curl build-essential libreadline-dev zlib1g-dev libsqlite3-dev libssl-dev libxml2-dev libxslt-dev autoconf automake bison libtool"
-	build_pkg_dependencies="$build_pkg_dependencies $build_ruby_dependencies"
+	build_pkg_dependencies="${build_pkg_dependencies:-} $build_ruby_dependencies"
 fi
 
 # Load the version of Ruby for an app, and set variables.