diff --git a/osf_tests/metrics/test_monthly_report.py b/osf_tests/metrics/test_monthly_report.py
index 0c0302a7f08..3c841e6555c 100644
--- a/osf_tests/metrics/test_monthly_report.py
+++ b/osf_tests/metrics/test_monthly_report.py
@@ -135,7 +135,7 @@ def test_with_last_month(self, osfid, this_month_report, last_month_report, two_
 
 def _prior_yearmonth(ym: YearMonth) -> YearMonth:
     return (
-        YearMonth(ym.year - 1, 1)
+        YearMonth(ym.year - 1, 12)
         if ym.month == 1
         else YearMonth(ym.year, ym.month - 1)
     )