diff --git a/src/headers/lex.hpp b/src/headers/lex.hpp
index c2eb211..fcb73fe 100644
--- a/src/headers/lex.hpp
+++ b/src/headers/lex.hpp
@@ -19,9 +19,9 @@ struct tok {
     };
     const type toktype;
     const std::string toktext;
-    const unsigned long line = 0;
-    tok(type Type, std::string_view Text, decltype(line) line): toktype(Type), toktext(Text), line(line) {}
-    explicit tok(type Type, decltype(line) line): tok(Type, std::string(1, Type), line) {};
+    const unsigned long line;
+    tok(const type& Type, std::string_view Text, const decltype(line)& line = 0): toktype(Type), toktext(Text), line(line) {}
+    explicit tok(const type& Type, const decltype(line)& line = 0): tok(Type, std::string(1, Type), line) {};
     friend std::ostream& operator<<(std::ostream& output, const tok& it) { return output << it.toktext; }
 };
 std::vector<tok> lex(const std::string& in);