diff --git a/include/dbus_monitor.hpp b/include/dbus_monitor.hpp
index 129422e..5f409d7 100644
--- a/include/dbus_monitor.hpp
+++ b/include/dbus_monitor.hpp
@@ -84,7 +84,7 @@
         }
 
         // data is type oa{sa{sv}} which is an array[2] of string, object
-        for (auto& entry : data[1].items())
+        for (const auto& entry : data[1].items())
         {
             auto it = thisSession->second.interfaces.find(entry.key());
             if (it != thisSession->second.interfaces.end())