diff --git a/data/helpers.d/php b/data/helpers.d/php
index 4c711056d..55c24ac57 100644
--- a/data/helpers.d/php
+++ b/data/helpers.d/php
@@ -2,7 +2,7 @@
 
 # Declare the actual php version to use.
 # A packager willing to use another version of php can override the variable into its _common.sh.
-if [ -n "$YNH_DEFAULT_PHP_VERSION" ]; then
+if [ -n "${YNH_DEFAULT_PHP_VERSION:-}" ]; then
 	YNH_PHP_VERSION=${YNH_PHP_VERSION:-YNH_DEFAULT_PHP_VERSION}
 fi