LibGDX Straight line is invisible

Question

I'm trying to draw a grid in libgdx, but I can't, becasue when I draw a striaght line it's invisible, O_O

public static void draw(ShapeRenderer render) {
    render.setColor(Color.WHITE);
    render.begin(ShapeType.Line);
    for(int r = 0; r < gridTiles.length; r++) {
        for(int c = 0; c < gridTiles[0].length; c++) {
            gridTiles[r][c].draw(render);
        }
    }
    render.end();
}

The draw() method

public void draw(ShapeRenderer render) {
    render.line(10, 10, 64, 10); // Invisible
}

however, if I change it to be slightly offset and not straight like

render.line(10, 10, 64, 9); // Visible

It becomes visible.