Add missing call to glutInit.
diff --git a/progs/demos/cubemap.c b/progs/demos/cubemap.c
index 0a59b98..ef5d235 100644
--- a/progs/demos/cubemap.c
+++ b/progs/demos/cubemap.c
@@ -454,6 +454,7 @@
 
 int main( int argc, char *argv[] )
 {
+   glutInit(&argc, argv);
    glutInitWindowPosition(0, 0);
    glutInitWindowSize(600, 500);
    glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE );