Count intersections of lines with polygon

I have the following problem in QGIS (2.6.0.)

I got a dataset of streets, which are displayed as linesegments. In another, independent dateset I have roundabouts as a point geometry.

Starting from this both datasets, I want to count the number of streets which lead to the roundabouts. I would start to make a buffer around the point-geometry of the roundabouts and afterwards intersect the buffer-polygon with the streets.

But how can I count the number of streets, which intersect with the buffer?