diff --git a/libavformat/ac4dec.c b/libavformat/ac4dec.c
index 71950f52dc..2952036c25 100644
--- a/libavformat/ac4dec.c
+++ b/libavformat/ac4dec.c
@@ -42,6 +42,8 @@ static int ac4_probe(const AVProbeData *p)
             size += 4;
             if (buf[1] == 0x41)
                 size += 2;
+            if (left < size)
+                break;
             max_frames++;
             left -= size;
             buf += size;