diff --git a/libavcodec/libaac_nextenc.c b/libavcodec/libaac_nextenc.c
index 3c34c24a63..f9d7706285 100755
--- a/libavcodec/libaac_nextenc.c
+++ b/libavcodec/libaac_nextenc.c
@@ -156,6 +156,7 @@ static av_cold int libaac_encode_init(AVCodecContext *avctx)
             return AVERROR(ENOMEM);
         }
 
+        avctx->extradata_size = s->encoder->ascSize;
         memcpy(avctx->extradata, s->encoder->asc, s->encoder->ascSize);
     }
     return 0;