diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
index 943c0278e5..30d1fcf4b7 100644
--- a/libavformat/flvdec.c
+++ b/libavformat/flvdec.c
@@ -1174,7 +1174,7 @@ retry_duration:
             avio_seek(s->pb, fsize - 3 - size, SEEK_SET);
             if (size == avio_rb24(s->pb) + 11) {
                 uint32_t ts = avio_rb24(s->pb);
-                ts         |= avio_r8(s->pb) << 24;
+                ts         |= (unsigned)avio_r8(s->pb) << 24;
                 if (ts)
                     s->duration = ts * (int64_t)AV_TIME_BASE / 1000;
                 else if (fsize >= 8 && fsize - 8 >= size) {