sass mixin with $var for Base64

I am trying to create simple mixin for my svg icons.

Mixin:

@mixin ico($position, $size, $image) {
    background-image: url(data:image/svg+xml;base64,$image);
    background-repeat: no-repeat;
    background-size : $size;
    background-position: $position;
    background-color: $blue-dark;
    height: 30px;
    padding-left: 30px;
}

SASS error:

"Syntax error: Invalid CSS after \"...image: url(data\": expected comma, was \":image/svg+xml;...\"\A

Not sure how to go around it.

Thanks for your help in advance.