diff --git a/src/policy_cache.hpp b/src/policy_cache.hpp
index 7fbc2206..8fd5d44a 100644
--- a/src/policy_cache.hpp
+++ b/src/policy_cache.hpp
@@ -20,7 +20,7 @@
 
 #include "nonstd/optional.hpp"
 #include "boost/unordered/concurrent_flat_map.hpp"
-#include "boost/flyweight
+#include "boost/flyweight.hpp"
 #include "wyhash.h"
 
 #include "fmt/core.h"