diff --git a/progs/redbook/feedback.c b/progs/redbook/feedback.c
index 4981854d95d..cc685d55d34 100644
--- a/progs/redbook/feedback.c
+++ b/progs/redbook/feedback.c
@@ -143,6 +143,8 @@ void display(void)
 
    size = glRenderMode (GL_RENDER);
    printBuffer (size, feedBuffer);
+
+   glFinish();
 }
 
 /* ARGSUSED1 */