diff --git a/src/Lexer.h b/src/Lexer.h
index 887f7f77fa..79efa5841b 100644
--- a/src/Lexer.h
+++ b/src/Lexer.h
@@ -18,7 +18,7 @@
 #define LEXER_H
 
 #include "support/strfwd.h"
-
+#include <string>
 
 namespace lyx {