diff --git a/libs/ardour/ardour/vst3_host.h b/libs/ardour/ardour/vst3_host.h
index 23ab0c2a7f..afc4755f2a 100644
--- a/libs/ardour/ardour/vst3_host.h
+++ b/libs/ardour/ardour/vst3_host.h
@@ -21,6 +21,7 @@
 
 #include <map>
 #include <vector>
+#include <string>
 #include <stdint.h>
 
 #include <glib.h>