diff --git a/Objects/bytes_methods.c b/Objects/bytes_methods.c
index 37c5f7dbc80..7d131842059 100644
--- a/Objects/bytes_methods.c
+++ b/Objects/bytes_methods.c
@@ -743,7 +743,7 @@ tailmatch(const char *str, Py_ssize_t len, PyObject *substr,
 
     if (direction < 0) {
         /* startswith */
-        if (start + slen > len)
+        if (start > len - slen)
             goto notfound;
     } else {
         /* endswith */