diff --git a/lib/config.js b/lib/config.js
index aeeb55e..0640cf5 100644
--- a/lib/config.js
+++ b/lib/config.js
@@ -542,7 +542,7 @@ util.loadFileConfigs = function(configDir, options) {
   var node_env_var_names = ['NODE_CONFIG_ENV', 'NODE_ENV'];
 
   // Loop through the variables to try and set environment
-  for (node_env_var_name of node_env_var_names) {
+  for (const node_env_var_name of node_env_var_names) {
     NODE_ENV = util.initParam(node_env_var_name);
     if (!!NODE_ENV) {
       NODE_ENV_VAR_NAME = node_env_var_name;