diff --git a/src/Format.h b/src/Format.h
index b4cc9f4fc4..99cc120748 100644
--- a/src/Format.h
+++ b/src/Format.h
@@ -16,6 +16,7 @@
 #include "support/trivstring.h"
 
 #include <vector>
+#include <string>
 
 namespace lyx {