Undefined index: geocoder_apikey_geocoder

I'm not sure if this error is occurring because of geocoder, or because of geofield's integration with geocoder, so I figured I'd throw it in here and it can get moved if need be. When I perform a search using geofield proximity field in views, all of the results show up just as they should, but I get an error of:

Notice: Undefined index: geocoder_apikey_yahoo in geocoder_yahoo() (line 27 of /Applications/MAMP/htdocs/sites/all/modules/geocoder/plugins/geocoder_handler/yahoo.inc).

I am using yahoo geocoding on both the geofields themselves and on the proximity filter. I've tried looking up how to use an API key for yahoo's service, but I haven't found anything helpful thus far. Any suggestions?