diff --git a/README.md b/README.md
index 837fd77..5f5b975 100644
--- a/README.md
+++ b/README.md
@@ -18,4 +18,8 @@ then install the dependencies
 pip install -r requirements.txt
 ```
 
+Dependencies are only `dnspython` and optionnally `iso8601` which is only
+required in re2oAPI.  The script runs fine with just `dnspython` as long as it
+does not stuple upon an error in the re2oAPI, which is should not according the
+tests.