diff --git a/libavformat/mov.c b/libavformat/mov.c
index 0b3380ea50..fc6006d28c 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -1568,7 +1568,7 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
                 stsc_index++;
             chunk_samples = sc->sample_to_chunk[stsc_index].count;
             /* get chunk size */
-            if (sc->sample_size > 1)
+            if (sc->sample_size > 1 || st->codec->bits_per_sample == 8)
                 chunk_size = chunk_samples * sc->sample_size;
             else if (sc->sample_size_v1.den > 0 && (chunk_samples * sc->sample_size_v1.num % sc->sample_size_v1.den == 0))
                 chunk_size = chunk_samples * sc->sample_size_v1.num / sc->sample_size_v1.den;