diff --git a/strings/ctype-simple.c b/strings/ctype-simple.c
index 5a5c363bbfbe..3e64004b8377 100644
--- a/strings/ctype-simple.c
+++ b/strings/ctype-simple.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2002, 2016, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2002, 2019, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -1517,7 +1517,7 @@ my_strntoull10rnd_8bit(const CHARSET_INFO *cs MY_ATTRIBUTE((unused)),
     str++;
     if (str < end)
     {
-      int negative_exp, exponent;
+      longlong negative_exp, exponent;
       if ((negative_exp= (*str == '-')) || *str=='+')
       {
         if (++str == end)
@@ -1527,7 +1527,10 @@ my_strntoull10rnd_8bit(const CHARSET_INFO *cs MY_ATTRIBUTE((unused)),
            str < end && (ch= (uchar) (*str - '0')) < 10;
            str++)
       {
-        exponent= exponent * 10 + ch;
+        if (exponent <= (LLONG_MAX - ch) / 10)
+         exponent= exponent * 10 + ch;
+        else
+         goto ret_too_big;
       }
       shift+= negative_exp ? -exponent : exponent;
     }