diff --git a/libavformat/jvdec.c b/libavformat/jvdec.c
index 21eb14d265..9053c61cf2 100644
--- a/libavformat/jvdec.c
+++ b/libavformat/jvdec.c
@@ -54,7 +54,7 @@ typedef struct {
 
 static int read_probe(AVProbeData *pd)
 {
-    if (pd->buf[0] == 'J' && pd->buf[1] == 'V' && strlen(MAGIC) <= pd->buf_size - 4 &&
+    if (pd->buf[0] == 'J' && pd->buf[1] == 'V' && strlen(MAGIC) + 4 <= pd->buf_size &&
         !memcmp(pd->buf + 4, MAGIC, strlen(MAGIC)))
         return AVPROBE_SCORE_MAX;
     return 0;