diff --git a/libavformat/isom.c b/libavformat/isom.c
index 6d019881e5..954ba1ec4f 100644
--- a/libavformat/isom.c
+++ b/libavformat/isom.c
@@ -358,6 +358,7 @@ int ff_mp4_read_dec_config_descr(AVFormatContext *fc, AVStream *st, AVIOContext
                                                 st->codecpar->extradata_size, 1, fc);
             if (ret < 0)
                 return ret;
+            av_channel_layout_uninit(&st->codecpar->ch_layout);
             st->codecpar->ch_layout.order = AV_CHANNEL_ORDER_UNSPEC;
             st->codecpar->ch_layout.nb_channels = cfg.channels;
             if (cfg.object_type == 29 && cfg.sampling_index < 3) // old mp3on4