diff --git a/libs/gtkmm2ext/gtkmm2ext/string_completion.h b/libs/gtkmm2ext/gtkmm2ext/string_completion.h
index 5c0ed5b1a8..2e8a81c4c5 100644
--- a/libs/gtkmm2ext/gtkmm2ext/string_completion.h
+++ b/libs/gtkmm2ext/gtkmm2ext/string_completion.h
@@ -21,10 +21,11 @@
 #include <vector>
 #include <ytkmm/entry.h>
 #include <ytkmm/liststore.h>
+#include "gtkmm2ext/visibility.h"
 
 namespace Gtkmm2ext {
 
-class StringCompletion : public Gtk::EntryCompletion
+class LIBGTKMM2EXT_API StringCompletion : public Gtk::EntryCompletion
 {
   public:
 	StringCompletion ();