diff --git a/examples/opengl/hellogl_es2/bubble.h b/examples/opengl/hellogl_es2/bubble.h
index cd4c8d91cc..b913d3620d 100644
--- a/examples/opengl/hellogl_es2/bubble.h
+++ b/examples/opengl/hellogl_es2/bubble.h
@@ -47,7 +47,7 @@
 #include <QRect>
 #include <QRectF>
 
-class QPainter;
+QT_FORWARD_DECLARE_CLASS(QPainter)
 
 class Bubble
 {
diff --git a/examples/opengl/hellogl_es2/mainwindow.h b/examples/opengl/hellogl_es2/mainwindow.h
index 7e16a6b6a7..4aac220692 100644
--- a/examples/opengl/hellogl_es2/mainwindow.h
+++ b/examples/opengl/hellogl_es2/mainwindow.h
@@ -43,9 +43,6 @@
 
 #include <QMainWindow>
 
-class QSlider;
-class GLWidget;
-
 class MainWindow : public QMainWindow
 {
     Q_OBJECT
diff --git a/examples/opengl/textures/glwidget.h b/examples/opengl/textures/glwidget.h
index 11a9818e19..757a7df627 100644
--- a/examples/opengl/textures/glwidget.h
+++ b/examples/opengl/textures/glwidget.h
@@ -44,7 +44,7 @@
 #include <QtWidgets>
 #include <QGLWidget>
 
-class QGLShaderProgram;
+QT_FORWARD_DECLARE_CLASS(QGLShaderProgram);
 
 class GLWidget : public QGLWidget
 {