diff --git a/.ci/atime/tests.R b/.ci/atime/tests.R
index b093e1e28..30a5d0e3a 100644
--- a/.ci/atime/tests.R
+++ b/.ci/atime/tests.R
@@ -212,6 +212,7 @@ test.list <- atime::atime_test_list(
 "forderv improved in #4386" = atime::atime_test(
   setup = {
     options(datatable.forder.auto.index = TRUE, datatable.forder.reuse.sorting = TRUE)
+    set.seed(1)
     dt <- data.table(index = sample(N), values = sample(N))
     data.table:::forderv(dt, "index") # Initial sort to create the index and initialize caching
   },