diff --git a/demos/cli.rb b/demos/cli.rb
index ada93cd..daf8182 100644
--- a/demos/cli.rb
+++ b/demos/cli.rb
@@ -1,7 +1,7 @@
 require 'geocoder/us/database'
 require 'pp'
 
-db = Geocoder::US::Database.new("/mnt/geocoder-us/geocoder.db", :debug=>true)
+db = Geocoder::US::Database.new("/mnt/tiger2010/geocoder.db", :debug=>true)
 result = db.geocode(ARGV[0])
 pp(result)
 print "#{result[0][:lat]} N, #{-result[0][:lon]} W\n"
diff --git a/lib/geocoder/us/database.rb b/lib/geocoder/us/database.rb
index be2b1fa..cb2c026 100644
--- a/lib/geocoder/us/database.rb
+++ b/lib/geocoder/us/database.rb
@@ -571,6 +571,7 @@ def interpolate (points, fraction, side, offset=0.000075)
       (1...points.length).each {|n| total += distance(points[n-1], points[n])}
       target = total * fraction
       for n in 1...points.length
+        next if points[n-1] == points[n] # because otherwise step==0 and dx/dy==NaN
         step = distance(points[n-1], points[n])
         if step < target
           target -= step
@@ -582,7 +583,9 @@ def interpolate (points, fraction, side, offset=0.000075)
           return street_side_offset(offset*side, points[n-1], found)
         end
       end
-     # raise "Can't happen!"
+      # in a pathological case, points[n-1] == points[n] for n==-1
+      # so *sigh* just forget interpolating and return points[-1]
+      return points[-1]
     end
 
     # Find and replace the city, state, and county information