diff --git a/virtualSensor.cpp b/virtualSensor.cpp
index 5883d23..304e874 100644
--- a/virtualSensor.cpp
+++ b/virtualSensor.cpp
@@ -292,7 +292,7 @@
     static constexpr auto exprKey = "Expression";
     if (sensorConfig.contains(exprKey))
     {
-        auto ref = sensorConfig.at(exprKey);
+        auto& ref = sensorConfig.at(exprKey);
         if (ref.is_array())
         {
             exprStr = std::string{};