Yep, Virgil only implicitly promotes integers to float when rounding won't change the value.

     // OK implicit promotions
     def x1: i20;
     def f1: float = x1;
     def x2: i21;
     def f2: float = x2;
     def x3: i22;
     def f3: float = x3;
     def x4: i23;
     def f4: float = x4;

     // compile error!
     def x5: i24;
     def f5: float = x5; // requires rounding

This also applies to casts, which are dynamically checked.

     // runtime error if rounding alters value
     def x5: i24;
     def f5: float = float.!(x5);