diff --git a/libavcodec/pcm.c b/libavcodec/pcm.c
index d8b013bcb0..3b61518509 100644
--- a/libavcodec/pcm.c
+++ b/libavcodec/pcm.c
@@ -209,7 +209,7 @@ static int pcm_encode_frame(AVCodecContext *avctx,
         break;
     case CODEC_ID_PCM_S24DAUD:
         for(;n>0;n--) {
-            uint32_t tmp = ff_reverse[*samples >> 8] +
+            uint32_t tmp = ff_reverse[(*samples >> 8) & 0xff] +
                            (ff_reverse[*samples & 0xff] << 8);
             tmp <<= 4; // sync flags would go here
             bytestream_put_be24(&dst, tmp);