diff --git a/src/policy_cache.hpp b/src/policy_cache.hpp
index 79277e77..46277c95 100644
--- a/src/policy_cache.hpp
+++ b/src/policy_cache.hpp
@@ -21,6 +21,8 @@
 #include "nonstd/optional.hpp"
 #include "boost/unordered/concurrent_flat_map.hpp"
 
+#include "fmt.hpp"
+
 #include <cstdint>
 #include <string>