diff --git a/src/Gui/View3DInventor.h b/src/Gui/View3DInventor.h
index 4f734c9d3..b0053e906 100644
--- a/src/Gui/View3DInventor.h
+++ b/src/Gui/View3DInventor.h
@@ -30,6 +30,7 @@
 #include <QImage>
 
 class SoNode;
+class QGLWidget;
 class QPrinter;
 class QStackedWidget;