diff --git a/main.cpp b/main.cpp
index d8b1135..ff0952d 100644
--- a/main.cpp
+++ b/main.cpp
@@ -158,7 +158,7 @@
      * however, a system isn't likely going to have more than a couple zones.
      * If it only has a couple zones, then this is fine.
      */
-    for (auto& i : zones)
+    for (const auto& i : zones)
     {
         std::cerr << "pushing zone" << std::endl;
         zoneThreads.push_back(std::thread(PIDControlThread, i.second.get()));