diff --git a/libavutil/lzo.c b/libavutil/lzo.c
index ef01653aa8..9cc82dce91 100644
--- a/libavutil/lzo.c
+++ b/libavutil/lzo.c
@@ -119,9 +119,8 @@ static inline void memcpy_backptr(uint8_t *dst, int back, int cnt);
  * thus creating a repeating pattern with a period length of back.
  */
 static inline void copy_backptr(LZOContext *c, int back, int cnt) {
-    register const uint8_t *src = &c->out[-back];
     register uint8_t *dst = c->out;
-    if (src < c->out_start || src > dst) {
+    if (dst - c->out_start < back) {
         c->error |= AV_LZO_INVALID_BACKPTR;
         return;
     }