diff --git a/src/common/PJoystickHandler.hxx b/src/common/PJoystickHandler.hxx
index 444ef1a6a..0d683e9aa 100644
--- a/src/common/PJoystickHandler.hxx
+++ b/src/common/PJoystickHandler.hxx
@@ -49,8 +49,8 @@ class PhysicalJoystickHandler
   private:
     struct StickInfo
     {
-      StickInfo(const nlohmann::json& map = nullptr, PhysicalJoystickPtr stick = nullptr)
-        : mapping(map), joy{std::move(stick)} { }
+      StickInfo(const nlohmann::json map, PhysicalJoystickPtr stick = nullptr)
+        : mapping(map), joy{std::move(stick)} {}
 
       nlohmann::json mapping;
       PhysicalJoystickPtr joy;