diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
index e0022f74f3..f4d5e58c54 100644
--- a/libavcodec/mpegvideo.c
+++ b/libavcodec/mpegvideo.c
@@ -229,8 +229,8 @@ int alloc_picture(MpegEncContext *s, Picture *pic, int shared){
 
         CHECKED_ALLOCZ(pic->mbskip_table , mb_array_size * sizeof(uint8_t)+2) //the +2 is for the slice end check
         CHECKED_ALLOCZ(pic->qscale_table , mb_array_size * sizeof(uint8_t))
-        CHECKED_ALLOCZ(pic->mb_type_base , big_mb_num    * sizeof(uint32_t))
-        pic->mb_type= pic->mb_type_base + s->mb_stride+1;
+        CHECKED_ALLOCZ(pic->mb_type_base , (big_mb_num + s->mb_stride) * sizeof(uint32_t))
+        pic->mb_type= pic->mb_type_base + 2*s->mb_stride+1;
         if(s->out_format == FMT_H264){
             for(i=0; i<2; i++){
                 CHECKED_ALLOCZ(pic->motion_val_base[i], 2 * (b4_array_size+4)  * sizeof(int16_t))