diff --git a/policy_table.hpp b/policy_table.hpp
index d6bf307..013578f 100644
--- a/policy_table.hpp
+++ b/policy_table.hpp
@@ -4,6 +4,7 @@
 
 #include <map>
 #include <optional>
+#include <string>
 #include <vector>
 
 namespace ibm