diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index bee8e89760..6dab5193b0 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -563,12 +563,12 @@ static int mov_write_eac3_tag(AVIOContext *pb, MOVTrack *track)
         put_bits(&pbc, 4, info->substream[i].num_dep_sub);
         if (!info->substream[i].num_dep_sub) {
             put_bits(&pbc, 1, 0); /* reserved */
-            size--;
         } else {
             put_bits(&pbc, 9, info->substream[i].chan_loc);
         }
     }
     flush_put_bits(&pbc);
+    size = put_bits_count(&pbc) >> 3;
 
     avio_wb32(pb, size + 8);
     ffio_wfourcc(pb, "dec3");
diff --git a/tests/ref/fate/copy-trac3074 b/tests/ref/fate/copy-trac3074
index 5ce5694260..ff66900253 100644
--- a/tests/ref/fate/copy-trac3074
+++ b/tests/ref/fate/copy-trac3074
@@ -1,5 +1,5 @@
-39aef1afff761d673fd1be07182941d1 *tests/data/fate/copy-trac3074.mp4
-333991 tests/data/fate/copy-trac3074.mp4
+f92a201033712bda262f1e071e25544a *tests/data/fate/copy-trac3074.mp4
+333992 tests/data/fate/copy-trac3074.mp4
 #tb 0: 1/48000
 #media_type 0: audio
 #codec_id 0: eac3