diff --git a/src/json.hpp b/src/json.hpp
index b357a70fb..2f0c8d5c9 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -300,7 +300,7 @@ class basic_json
     */
     friend bool operator<(const value_t lhs, const value_t rhs)
     {
-        std::array<uint8_t, 7> order = {{
+        static constexpr std::array<uint8_t, 7> order = {{
                 0, // null
                 3, // object
                 4, // array