Error in calc()

[fedorovsky]

This code throws a compilation error:

:root {
    --variable-top: 50px;
}

.some-class {
    margin-top: calc(-1 * var(--variable-top)); 
}

The problem is -1. But my code above is valid. But if I change -1 to -1px, it works

margin-top: calc(-1px * var(--variable-top));