diff --git a/libultraship/libultraship/File.h b/libultraship/libultraship/File.h
index d4042948bf7..03f08c80f76 100644
--- a/libultraship/libultraship/File.h
+++ b/libultraship/libultraship/File.h
@@ -3,6 +3,7 @@
 #include <string>
 #include <memory>
 #include <mutex>
+#include <condition_variable>
 
 namespace Ship {
 	class Archive;