diff --git a/libav/wav.c b/libav/wav.c
index c3a430df5405ec8bef792e3733d73e3bb35bbd48..70a0e41b41475e2e1a983b6629697b9e22de2055 100644
--- a/libav/wav.c
+++ b/libav/wav.c
@@ -72,7 +72,7 @@ static int wav_write_trailer(AVFormatContext *s)
         /* update file size */
         file_size = url_ftell(pb);
         url_fseek(pb, 4, SEEK_SET);
-        put_le32(pb, (UINT32)file_size);
+        put_le32(pb, (UINT32)(file_size - 8));
         url_fseek(pb, file_size, SEEK_SET);
 
         put_flush_packet(pb);