diff --git a/src/cpp/ripple/PathDB.h b/src/cpp/ripple/PathDB.h
index 522e0a8f64..59a4d5747f 100644
--- a/src/cpp/ripple/PathDB.h
+++ b/src/cpp/ripple/PathDB.h
@@ -1,6 +1,8 @@
 #ifndef PATHDB__H
 #define PATHBD__H
 
+#include <set>
+
 #include "uint256.h"
 #include "TaggedCache.h"