diff --git a/demux/demux_lavf.c b/demux/demux_lavf.c
index d8e8109c93..48e79e949b 100644
--- a/demux/demux_lavf.c
+++ b/demux/demux_lavf.c
@@ -267,12 +267,11 @@ static int lavf_check_file(demuxer_t *demuxer)
     while (avpd.buf_size < PROBE_BUF_SIZE) {
         int nsize = av_clip(avpd.buf_size * 2, INITIAL_PROBE_SIZE,
                             PROBE_BUF_SIZE);
-        int read_size = stream_read(s, avpd.buf + avpd.buf_size,
-                                    nsize - avpd.buf_size);
-        if (read_size <= 0)
+        bstr buf = stream_peek(s, nsize);
+        if (buf.len <= avpd.buf_size)
             break;
-
-        avpd.buf_size += read_size;
+        memcpy(avpd.buf, buf.start, buf.len);
+        avpd.buf_size = buf.len;
 
         int score = 0;
         priv->avif = av_probe_input_format2(&avpd, avpd.buf_size > 0, &score);
@@ -294,7 +293,6 @@ static int lavf_check_file(demuxer_t *demuxer)
         priv->avif = NULL;
     }
 
-    stream_unread_buffer(s, avpd.buf, avpd.buf_size);
     av_free(avpd.buf);
 
     if (!priv->avif) {