diff --git a/libavcodec/movsub_bsf.c b/libavcodec/movsub_bsf.c
index 5878607061..cd48aa7bb8 100644
--- a/libavcodec/movsub_bsf.c
+++ b/libavcodec/movsub_bsf.c
@@ -75,8 +75,8 @@ static int mov2textsub(AVBSFContext *ctx, AVPacket *pkt)
        return AVERROR_INVALIDDATA;
     }
 
-    pkt->data += 2;
     pkt->size  = FFMIN(pkt->size - 2, AV_RB16(pkt->data));
+    pkt->data += 2;
 
     return 0;
 }