diff --git a/libs/canvas/canvas/widget.h b/libs/canvas/canvas/widget.h
index c322901d3a..b54db86d8e 100644
--- a/libs/canvas/canvas/widget.h
+++ b/libs/canvas/canvas/widget.h
@@ -24,7 +24,7 @@
 #include "canvas/visibility.h"
 #include "canvas/item.h"
 
-#include "gtkmm2ext/cairo_widget.h"
+class CairoWidget; /* should really be in Gtkmm2ext namespace */
 
 namespace ArdourCanvas
 {
diff --git a/libs/canvas/widget.cc b/libs/canvas/widget.cc
index 19c7e76ea0..bb33796528 100644
--- a/libs/canvas/widget.cc
+++ b/libs/canvas/widget.cc
@@ -26,6 +26,8 @@
 #include "canvas/widget.h"
 #include "canvas/debug.h"
 
+#include "gtkmm2ext/cairo_widget.h"
+
 using namespace std;
 using namespace ArdourCanvas;