Warning: number_format() expects parameter 1 to be double

I ran into this error when I was working on the Google Custom Search API.  I've never run into it before.  I'm passing the estimated number of search results through to a number_format() which is currently passing through the number 10.  Unfortunately it's throwing this error.  I haven't figured it out yet, if anyone knows please post the solution so others can find it as well.