diff --git a/src/lib/format-time.js b/src/lib/format-time.js
index 10b19882f..b4f7eaba2 100644
--- a/src/lib/format-time.js
+++ b/src/lib/format-time.js
@@ -1,3 +1,6 @@
+// IMPORTANT: any changes to the time algorithm also need to be made in the corresponding
+// scratchr2 file 'lib/format-time.js'
+
 /**
  Given a timestamp in the future, calculate the largest, closest unit to show.
  On the high end we stop at hours. e.g. 15 days is still counted in hours not days or weeks.