diff --git a/gap/bytable.gi b/gap/bytable.gi
index f5d1075..e69410d 100644
--- a/gap/bytable.gi
+++ b/gap/bytable.gi
@@ -52,7 +52,7 @@ NextMagmaString@ := function(filts)
   n := MagmaNumber@;
   MagmaNumber@ := MagmaNumber@ + 1;
   while n > 0 do
-    Add(str, MagmaLetters[RemInt(n, MagmaBase@) + 1]);
+    Add(str, MagmaLetters@[RemInt(n, MagmaBase@) + 1]);
     n := QuoInt(n, MagmaBase@);
   od;
   return str;