rounding error interrupts GPXViewer

Upon opening a .gpx file I got the message :

$ gpxviewer
Traceback (most recent call last):
  File "/usr/share/gpxviewer/gpxviewer/ui.py", line 300, in onTrackAdded
    self.selectTrace(trace)
  File "/usr/share/gpxviewer/gpxviewer/ui.py", line 347, in selectTrace
    distance = trace.get_distance()
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 153, in get_distance
    return self._get_cached_value("distance")
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 99, in _get_cached_value
    self._walk_points()
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 75, in _walk_points
    d = calculate_distance(point['lat'], pointp['lat'], point['lon'], pointp['lon'])
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 36, in calculate_distance
    arc = acos((sin(lat1) * sin(lat2)) + (cos(lat1) * cos(lat2) * cos(lon2 - lon1)))
ValueError: math domain error

I inserted the line :

print "lat1=",lat1, "lat2=",lat2, "lon1=",lon1, "lon2=",lon2

And got :

.....
lat1= -22.951462 lat2= -22.951447 lon1= -43.356941 lon2= -43.356937
lat1= -22.951469 lat2= -22.951462 lon1= -43.356941 lon2= -43.356941
lat1= -22.951469 lat2= -22.951469 lon1= -43.356941 lon2= -43.356941
Traceback (most recent call last):
  File "/usr/share/gpxviewer/gpxviewer/ui.py", line 300, in onTrackAdded
    self.selectTrace(trace)
  File "/usr/share/gpxviewer/gpxviewer/ui.py", line 347, in selectTrace
    distance = trace.get_distance()
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 156, in get_distance
    return self._get_cached_value("distance")
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 102, in _get_cached_value
    self._walk_points()
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 78, in _walk_points
    d = calculate_distance(point['lat'], pointp['lat'], point['lon'], pointp['lon'])
  File "/usr/share/gpxviewer/gpxviewer/gpx.py", line 39, in calculate_distance
    arc = acos((sin(lat1) * sin(lat2)) + (cos(lat1) * cos(lat2) * cos(lon2 - lon1)))
ValueError: math domain error

Interactively computing the value I got :

>>> ((sin(lat1) * sin(lat2)) + (cos(lat1) * cos(lat2) * cos(lon2 - lon1)))
1.0000000000000002

This seems to be a typical perversion of floating point rounding error. Do not seems too complicated to fix.

Something like the patch I am attaching.