diff --git a/libavcodec/g729_parser.c b/libavcodec/g729_parser.c
index 8c06ce4ee6..4dcdeab651 100644
--- a/libavcodec/g729_parser.c
+++ b/libavcodec/g729_parser.c
@@ -48,6 +48,9 @@ static int g729_parse(AVCodecParserContext *s1, AVCodecContext *avctx,
         s->block_size = (avctx->bit_rate < 8000) ? G729D_6K4_BLOCK_SIZE : G729_8K_BLOCK_SIZE;
         if (avctx->codec_id == AV_CODEC_ID_ACELP_KELVIN)
             s->block_size++;
+        // channels > 2 is invalid, we pass the packet on unchanged
+        if (avctx->channels > 2)
+            s->block_size = 0;
         s->block_size *= avctx->channels;
         s->duration   = avctx->frame_size;
     }