diff --git a/renrs/src/parser/event.rs b/renrs/src/parser/event.rs
index 53abb11..b2344d9 100644
--- a/renrs/src/parser/event.rs
+++ b/renrs/src/parser/event.rs
@@ -34,7 +34,7 @@ fn interpolate_string(input: &str, variables: &HashMap<String, Token>) -> String
         if let Some(value) = variables.get(var_name) {
             value.to_string()
         } else {
-            format!("[{}]", var_name)
+            panic!("undefined variable `{var_name}`");
         }
     });