diff --git a/src/settings.rs b/src/settings.rs
index 22ec9024..837e2bab 100644
--- a/src/settings.rs
+++ b/src/settings.rs
@@ -112,7 +112,7 @@ impl Settings {
             log::warn!("configuration file not found");
         }
 
-        s.merge(Environment::with_prefix("GUARD"))?;
+        s.merge(Environment::with_prefix("GUARD").separator("_"))?;
 
         check_url(&s);