diff --git a/libavformat/tty.c b/libavformat/tty.c
index 60f7e9f87e..854a23c500 100644
--- a/libavformat/tty.c
+++ b/libavformat/tty.c
@@ -53,6 +53,9 @@ static int read_probe(const AVProbeData *p)
 {
     int cnt = 0;
 
+    if (!p->buf_size)
+        return 0;
+
     for (int i = 0; i < p->buf_size; i++)
         cnt += !!isansicode(p->buf[i]);