diff --git a/src/policy_cache.hpp b/src/policy_cache.hpp
index 8a3dc54c..1b2c01c2 100644
--- a/src/policy_cache.hpp
+++ b/src/policy_cache.hpp
@@ -21,6 +21,7 @@
 #include "nonstd/optional.hpp"
 #include "boost/unordered/concurrent_flat_map.hpp"
 #include "boost/flyweight/flyweight.hpp"
+#include "boost/flyweight/no_tracking.hpp"
 #include "wyhash.h"
 
 #include "fmt/core.h"