diff --git a/libs/gtkmm2ext/utils.cc b/libs/gtkmm2ext/utils.cc
index c10497a8fb..147256b426 100644
--- a/libs/gtkmm2ext/utils.cc
+++ b/libs/gtkmm2ext/utils.cc
@@ -20,6 +20,7 @@
 
 #include <map>
 #include <algorithm>
+#include <iostream>
 
 #include <gtk/gtkpaned.h>
 #include <gtk/gtk.h>