diff --git a/lib/geocoder/calculations.rb b/lib/geocoder/calculations.rb
index a3c69ce8808eba4179b32bf6f03ee6a833dcd988..8375a0f7b9fc33abfcb1c90bccdb158933550c4e 100644
--- a/lib/geocoder/calculations.rb
+++ b/lib/geocoder/calculations.rb
@@ -118,9 +118,10 @@ module Geocoder
 
     ##
     # Radius of the earth, in miles.
+    # Taken from: http://en.wikipedia.org/wiki/Earth_radius
     #
     def earth_radius
-      3956
+      3959.0
     end
 
     ##