Meta description in article (CMS)

[ablaye]

When I post an article in the CMS and I don't fill in the meta description field, the meta description field ends up with some random words from the article.
For example, if you take a look at the HTML source code of http://www.ndakaru.com/content/264 you can clearly see that the meta description has some words in it. I didn't put those words there and I don't like the random words that were included there.

I don't want to have to write everything in the meta description field when I post articles. I would like the meta description, instead of filling up with random words taken from the article, to have the first few sentences of the article.

Is there any way to do this or at least prevent the nonsense text that is copied there by default?

Thanks