diff --git a/libs/surfaces/control_protocol/control_protocol.cc b/libs/surfaces/control_protocol/control_protocol.cc
index 36131e0b9e..ac244860b1 100644
--- a/libs/surfaces/control_protocol/control_protocol.cc
+++ b/libs/surfaces/control_protocol/control_protocol.cc
@@ -18,6 +18,7 @@
 
 */
 
+#include "pbd/convert.h"
 #include "pbd/error.h"
 
 #include "ardour/gain_control.h"