diff --git a/libavcodec/zmbvenc.c b/libavcodec/zmbvenc.c
index fbefa7cafc..0bf1dff192 100644
--- a/libavcodec/zmbvenc.c
+++ b/libavcodec/zmbvenc.c
@@ -246,7 +246,7 @@ static av_cold int encode_init(AVCodecContext *avctx)
     int lvl = 9;
 
     for(i=1; i<256; i++)
-        score_tab[i]= -i * log2(i/256.0) * 256;
+        score_tab[i]= -i * log2(i/(double)(ZMBV_BLOCK*ZMBV_BLOCK)) * 256;
 
     c->avctx = avctx;