diff --git a/bids-validator/utils/issues/list.js b/bids-validator/utils/issues/list.js
index 143e30689..ea875278b 100644
--- a/bids-validator/utils/issues/list.js
+++ b/bids-validator/utils/issues/list.js
@@ -466,7 +466,7 @@ export default {
     key: 'ACQTIME_FMT',
     severity: 'error',
     reason:
-      'Entries in the "acq_time" column of _scans.tsv should be expressed in the following format YYYY-MM-DDTHH:mm:ss (year, month, day, hour (24h), minute, second; this is equivalent to the RFC3339 “date-time” format. ',
+      'Entries in the "acq_time" column of _scans.tsv should be expressed in the following format YYYY-MM-DDTHH:mm:ss[.000000] (year, month, day, hour (24h), minute, second, and optionally fractional second; this is equivalent to the RFC3339 "date-time" format.',
   },
   85: {
     key: 'SUSPICIOUSLY_LONG_EVENT_DESIGN',