diff --git a/libs/ardour/vst_plugin.cc b/libs/ardour/vst_plugin.cc
index b92cad853a..edbf773e21 100644
--- a/libs/ardour/vst_plugin.cc
+++ b/libs/ardour/vst_plugin.cc
@@ -30,6 +30,7 @@
 #include <sys/stat.h>
 #include <cerrno>
 
+#include <glibmm/ustring.h>
 #include <glibmm/miscutils.h>
 
 #include <lrdf.h>