diff --git a/libavcodec/smvjpegdec.c b/libavcodec/smvjpegdec.c
index 9057e86161..e319e5781b 100644
--- a/libavcodec/smvjpegdec.c
+++ b/libavcodec/smvjpegdec.c
@@ -152,6 +152,10 @@ static int smvjpeg_decode_frame(AVCodecContext *avctx, void *data, int *data_siz
 
     cur_frame = avpkt->pts % s->frames_per_jpeg;
 
+    /* cur_frame is later used to calculate the buffer offset, so it mustn't be negative */
+    if (cur_frame < 0)
+        cur_frame += s->frames_per_jpeg;
+
     /* Are we at the start of a block? */
     if (!cur_frame) {
         av_frame_unref(mjpeg_data);