diff --git a/sql/filesort.cc b/sql/filesort.cc
index 0bae98f06e8..16fc845f5d2 100644
--- a/sql/filesort.cc
+++ b/sql/filesort.cc
@@ -370,7 +370,7 @@ static BUFFPEK *read_buffpek_from_file(IO_CACHE *buffpek_pointers, uint count)
   ulong length;
   BUFFPEK *tmp;
   DBUG_ENTER("read_buffpek_from_file");
-  if (count > ULONG_MAX/sizeof(BUFFPEK))
+  if ((ulong)count > ULONG_MAX/sizeof(BUFFPEK))
     return 0; /* sizeof(BUFFPEK)*count will overflow */
   tmp=(BUFFPEK*) my_malloc(length=sizeof(BUFFPEK)*count, MYF(MY_WME));
   if (tmp)