diff --git a/src/OpenMesh/Apps/QtViewer/MeshViewerWidgetT.hh b/src/OpenMesh/Apps/QtViewer/MeshViewerWidgetT.hh
index dc7dd987..8d073e4b 100644
--- a/src/OpenMesh/Apps/QtViewer/MeshViewerWidgetT.hh
+++ b/src/OpenMesh/Apps/QtViewer/MeshViewerWidgetT.hh
@@ -57,6 +57,7 @@
 #include <OpenMesh/Tools/Utils/Timer.hh>
 #include <OpenMesh/Apps/QtViewer/QGLViewerWidget.hh>
 
+#include <GL/gl.h>
 
 //== FORWARDS =================================================================
 
diff --git a/src/OpenMesh/Apps/QtViewer/QGLViewerWidget.hh b/src/OpenMesh/Apps/QtViewer/QGLViewerWidget.hh
index 7b46cd41..4b65cc73 100644
--- a/src/OpenMesh/Apps/QtViewer/QGLViewerWidget.hh
+++ b/src/OpenMesh/Apps/QtViewer/QGLViewerWidget.hh
@@ -57,6 +57,8 @@
     #include <QtOpenGLWidgets/QOpenGLWidget>
 #endif
 
+#include <GL/gl.h>
+
 //== FORWARD DECLARATIONS =====================================================
 
 class QMenu;