[Lazarus] Warning about integer constant and expression

[Jürgen Hestermann]

WIth this definition:

var  i64 : Int64;

and this code:

if i64>High(SizeInt) then

I get:
"Warning: Comparison might be always false due to range of constant and expression"
And even more strange, if I convert the constant to int64 as in

if i64>int64(High(SizeInt)) then

I still get this warning.
Why?