diff --git a/doc/examples/muxing.c b/doc/examples/muxing.c
index f1f5bb8239..1df5912ca7 100644
--- a/doc/examples/muxing.c
+++ b/doc/examples/muxing.c
@@ -440,15 +440,7 @@ static void open_video(AVFormatContext *oc, AVCodec *codec, OutputStream *ost, A
 static void fill_yuv_image(AVFrame *pict, int frame_index,
                            int width, int height)
 {
-    int x, y, i, ret;
-
-    /* when we pass a frame to the encoder, it may keep a reference to it
-     * internally;
-     * make sure we do not overwrite it here
-     */
-    ret = av_frame_make_writable(pict);
-    if (ret < 0)
-        exit(1);
+    int x, y, i;
 
     i = frame_index;
 
@@ -475,6 +467,11 @@ static AVFrame *get_video_frame(OutputStream *ost)
                       STREAM_DURATION, (AVRational){ 1, 1 }) >= 0)
         return NULL;
 
+    /* when we pass a frame to the encoder, it may keep a reference to it
+     * internally; make sure we do not overwrite it here */
+    if (av_frame_make_writable(ost->frame) < 0)
+        exit(1);
+
     if (c->pix_fmt != AV_PIX_FMT_YUV420P) {
         /* as we only generate a YUV420P picture, we must convert it
          * to the codec pixel format if needed */