diff --git a/progs/demos/osdemo16.c b/progs/demos/osdemo16.c
index f2f321b9b3e..6f892620ce6 100644
--- a/progs/demos/osdemo16.c
+++ b/progs/demos/osdemo16.c
@@ -128,6 +128,11 @@ static void render_image( void )
 
    glPopMatrix();
 
+   /* This is very important!!!
+    * Make sure buffered commands are finished!!!
+    */
+   glFinish();
+
    gluDeleteQuadric(qobj);
 
    {
diff --git a/progs/demos/osdemo32.c b/progs/demos/osdemo32.c
index 66e821ad4e8..b425a56c848 100644
--- a/progs/demos/osdemo32.c
+++ b/progs/demos/osdemo32.c
@@ -127,6 +127,11 @@ static void render_image( void )
 
    glPopMatrix();
 
+   /* This is very important!!!
+    * Make sure buffered commands are finished!!!
+    */
+   glFinish();
+
    gluDeleteQuadric(qobj);
 
    {