diff --git a/src/json.hpp b/src/json.hpp
index 6dfc1831..6be0a2bf 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -12477,7 +12477,7 @@ basic_json_parser_74:
         // the valid JSON Patch operations
         enum class patch_operations {add, remove, replace, move, copy, test, invalid};
 
-        const auto get_op = [](const std::string op)
+        const auto get_op = [](const std::string & op)
         {
             if (op == "add")
             {
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index a42daba6..0d6e9dab 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -11511,7 +11511,7 @@ class basic_json
         // the valid JSON Patch operations
         enum class patch_operations {add, remove, replace, move, copy, test, invalid};
 
-        const auto get_op = [](const std::string op)
+        const auto get_op = [](const std::string & op)
         {
             if (op == "add")
             {