diff --git a/tools/invite2summit/README.rst b/tools/invite2summit/README.rst
index b2b4d7be9f..e31c4fde85 100644
--- a/tools/invite2summit/README.rst
+++ b/tools/invite2summit/README.rst
@@ -10,6 +10,11 @@ You use it like this:
 - Copy settings.py.sample to settings.py
 - Update values in settings.py, especially *EMAIL_USER*, *EMAIL_FROM*,
   *EMAIL_SIGNATURE* and *EMAIL_PASSWORD*
+- Note that literal ``$`` characters in the template which are not part
+  of a substitution variable (such as dollar amounts) should be doubled
+  to escape them like ``... a $$600-off discount code ...`` so as to
+  avoid raising *ValueError: Invalid placeholder in string: line <X>,
+  col <Y>*
 - Run a test with ``python send.py atc_sample.csv codes_sample.csv``
 
 Should work on stock Ubuntu.