diff --git a/server/lib/python/cartodb_services/README.md b/server/lib/python/cartodb_services/README.md
index 5cac032..5b52f3d 100644
--- a/server/lib/python/cartodb_services/README.md
+++ b/server/lib/python/cartodb_services/README.md
@@ -24,7 +24,7 @@ NOTE: a system installation is required at present because the library is meant
 
 
 ## Running the unit tests
-Just run `nosetests test/`
+Just run `MAPBOX_API_KEY=xxx nosetests test/`
 ```shell
 $ nosetests test/
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