diff --git a/src/realm/db.hpp b/src/realm/db.hpp
index 7613a4c367b..99a223b5d1a 100644
--- a/src/realm/db.hpp
+++ b/src/realm/db.hpp
@@ -37,6 +37,7 @@
 #include <cstdint>
 #include <limits>
 #include <condition_variable>
+#include <unordered_map>
 
 namespace realm {