diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim.kshlib b/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim.kshlib
index 1c54c66c1..e8d43cc8c 100644
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim.kshlib
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim.kshlib
@@ -30,6 +30,23 @@ function trim_progress # pool disk
 	trim_prog_line "$1" "$2" | sed 's/.*(\([0-9]\{1,\}\)% trimmed.*/\1/g'
 }
 
+#
+# Write a bit of data and sync several times.
+#
+function sync_and_rewrite_some_data_a_few_times
+{
+	typeset pool=$1
+	typeset -i a_few_times=${2:-20}
+
+	typeset file="/$pool/tmpfile"
+	for i in {0..$a_few_times}; do
+		dd if=/dev/urandom of=${file} bs=128k count=10
+		sync_pool "$pool"
+	done
+
+	return 0
+}
+
 function cleanup
 {
 	if poolexists $TESTPOOL; then
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_online_offline.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_online_offline.ksh
index 681cd12f7..afc9a2ed1 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_online_offline.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_online_offline.ksh
@@ -27,7 +27,7 @@
 # Trimming automatically resumes across offline/online.
 #
 # STRATEGY:
-# 1. Create a pool with a two-way mirror.
+# 1. Create a pool with a two-way mirror, prepare blocks to trim.
 # 2. Start trimming one of the disks and verify that trimming is active.
 # 3. Offline the disk.
 # 4. Online the disk.
@@ -39,8 +39,10 @@
 DISK1=${DISKS%% *}
 DISK2="$(echo $DISKS | cut -d' ' -f2)"
 
-log_must zpool create -f $TESTPOOL mirror $DISK1 $DISK2
-log_must zpool trim -r 128M $TESTPOOL $DISK1
+log_must zpool create -f $TESTPOOL mirror $DISK1 $DISK2 -O recordsize=4k
+sync_and_rewrite_some_data_a_few_times $TESTPOOL
+
+log_must zpool trim -r 1 $TESTPOOL $DISK1
 
 log_must zpool offline $TESTPOOL $DISK1
 
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_start_and_cancel_neg.ksh b/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_start_and_cancel_neg.ksh
index faf134fbb..68e990900 100755
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_start_and_cancel_neg.ksh
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_trim/zpool_trim_start_and_cancel_neg.ksh
@@ -39,8 +39,10 @@ DISK2="$(echo $DISKS | cut -d' ' -f2)"
 DISK3="$(echo $DISKS | cut -d' ' -f3)"
 
 log_must zpool list -v
-log_must zpool create -f $TESTPOOL $DISK1 $DISK2 $DISK3
-log_must zpool trim -r 128M $TESTPOOL $DISK1
+log_must zpool create -f $TESTPOOL $DISK1 $DISK2 $DISK3 -O recordsize=4k
+sync_and_rewrite_some_data_a_few_times $TESTPOOL
+
+log_must zpool trim -r 1 $TESTPOOL $DISK1
 
 [[ -z "$(trim_progress $TESTPOOL $DISK1)" ]] && \
     log_fail "Trim did not start"