diff --git a/include/db_types.hpp b/include/db_types.hpp
index 5dcff65..5230217 100644
--- a/include/db_types.hpp
+++ b/include/db_types.hpp
@@ -78,7 +78,7 @@ inline bool operator!=(int const & lhs, uuid_t const & rhs) {
 
 
 // easier conversion to string
-inline std::string to_string(uuid_t const &value) {
+inline std::string to_string(const uuid_t& value) {
     std::ostringstream uuid_s;
     uuid_s << std::hex;
     uuid_s << std::setfill('0') << std::setw(16) << value.uuid_upper;
@@ -87,7 +87,7 @@ inline std::string to_string(uuid_t const &value) {
 }
 
 // stream operations
-inline std::ostream& operator<<(std::ostream& os, uuid_t& value) {
+inline std::ostream& operator<<(std::ostream& os, const uuid_t& value) {
     os << to_string(value);
     return os;
 };