diff --git a/lib/parser/builders/default.rb b/lib/parser/builders/default.rb
index e5c2107cf..25cb02d0c 100644
--- a/lib/parser/builders/default.rb
+++ b/lib/parser/builders/default.rb
@@ -1724,7 +1724,7 @@ def arg_name_collides?(this_name, that_name)
     end
 
     def check_lvar_name(name, loc)
-      if name =~ /\A[[[:lower:]]|_][[[:alnum:]]_]*\z/
+      if name =~ /\A[[[:lower:]]_][[[:alnum:]]_]*\z/
         # OK
       else
         diagnostic :error, :lvar_name, { name: name }, loc