class MyClass(T) : Base if (ConstraintExpression) {} compilation error

[ref2401]

Version D 2.062

Please explain what is causing the error

class Base
{ }

class Class(T) : Base
if (is(T == int))
{ }

Error: unrecognized declaration
Error: members expected
Error: Declaration expected, not 'if'
Error: { } expected following aggregate declaration