diff --git a/source/code/code.cpp b/source/code/code.cpp
index a42e8a8..d496605 100644
--- a/source/code/code.cpp
+++ b/source/code/code.cpp
@@ -9,7 +9,7 @@
 #include <fmt/core.h>
 #include <fmt/format.h>
 
-auto operator<<(std::ostream& ostream, const opcodes& opcode) -> std::ostream&
+auto operator<<(std::ostream& ostream, opcodes opcode) -> std::ostream&
 {
     using enum opcodes;
     switch (opcode) {
diff --git a/source/code/code.hpp b/source/code/code.hpp
index ec093da..1569b30 100644
--- a/source/code/code.hpp
+++ b/source/code/code.hpp
@@ -45,7 +45,7 @@ enum class opcodes : uint8_t
     current_closure,
 };
 
-auto operator<<(std::ostream& ostream, const opcodes& opcode) -> std::ostream&;
+auto operator<<(std::ostream& ostream, opcodes opcode) -> std::ostream&;
 
 using operands = std::vector<size_t>;
 using instructions = std::vector<uint8_t>;
diff --git a/source/lexer/token_type.cpp b/source/lexer/token_type.cpp
index bad9cb6..0afa0cc 100644
--- a/source/lexer/token_type.cpp
+++ b/source/lexer/token_type.cpp
@@ -1,6 +1,6 @@
 #include "token_type.hpp"
 
-auto operator<<(std::ostream& ostream, const token_type& type) -> std::ostream&
+auto operator<<(std::ostream& ostream, token_type type) -> std::ostream&
 {
     switch (type) {
         case token_type::asterisk:
diff --git a/source/lexer/token_type.hpp b/source/lexer/token_type.hpp
index ab5c16a..df9676d 100644
--- a/source/lexer/token_type.hpp
+++ b/source/lexer/token_type.hpp
@@ -55,4 +55,4 @@ enum class token_type
     ret,
 };
 
-auto operator<<(std::ostream& ostream, const token_type& type) -> std::ostream&;
+auto operator<<(std::ostream& ostream, token_type type) -> std::ostream&;