diff --git a/libavcodec/mjpegenc.c b/libavcodec/mjpegenc.c
index 7487ef8f66..842528e5f1 100644
--- a/libavcodec/mjpegenc.c
+++ b/libavcodec/mjpegenc.c
@@ -487,7 +487,7 @@ static void encode_block(MpegEncContext *s, int16_t *block, int n)
         put_bits(&s->pb, huff_size_ac[0], huff_code_ac[0]);
 }
 
-void ff_mjpeg_encode_mb(MpegEncContext *s, int16_t block[6][64])
+void ff_mjpeg_encode_mb(MpegEncContext *s, int16_t block[12][64])
 {
     int i;
     if (s->chroma_format == CHROMA_444) {
diff --git a/libavcodec/mjpegenc.h b/libavcodec/mjpegenc.h
index c5b05b511b..94bb652fba 100644
--- a/libavcodec/mjpegenc.h
+++ b/libavcodec/mjpegenc.h
@@ -61,6 +61,6 @@ void ff_mjpeg_encode_stuffing(MpegEncContext *s);
 void ff_mjpeg_init_hvsample(AVCodecContext *avctx, int hsample[3], int vsample[3]);
 void ff_mjpeg_encode_dc(PutBitContext *pb, int val,
                         uint8_t *huff_size, uint16_t *huff_code);
-void ff_mjpeg_encode_mb(MpegEncContext *s, int16_t block[6][64]);
+void ff_mjpeg_encode_mb(MpegEncContext *s, int16_t block[12][64]);
 
 #endif /* AVCODEC_MJPEGENC_H */