diff --git a/src/Fields/Field.php b/src/Fields/Field.php
index d92d54d..dfd5c18 100644
--- a/src/Fields/Field.php
+++ b/src/Fields/Field.php
@@ -223,7 +223,7 @@ public function asLineMarc(string $sep = '$', string $blank = ' '): ?string
             $ind2 = $blank;
         }
 
-        return "${tag} ${ind1}${ind2} " . implode(' ', $subfields);
+        return "{$tag} {$ind1}{$ind2} " . implode(' ', $subfields);
     }
 
     /**