diff --git a/tests/zfs-tests/include/commands.cfg b/tests/zfs-tests/include/commands.cfg
index 113b83c759..e6f04060ca 100644
--- a/tests/zfs-tests/include/commands.cfg
+++ b/tests/zfs-tests/include/commands.cfg
@@ -10,6 +10,7 @@
 export SYSTEM_FILES='arp
     awk
     attr
+    base64
     basename
     bc
     blkid
diff --git a/tests/zfs-tests/tests/functional/rsend/send-cD.ksh b/tests/zfs-tests/tests/functional/rsend/send-cD.ksh
index c51788f810..ceface9dbc 100755
--- a/tests/zfs-tests/tests/functional/rsend/send-cD.ksh
+++ b/tests/zfs-tests/tests/functional/rsend/send-cD.ksh
@@ -12,7 +12,7 @@
 #
 
 #
-# Copyright (c) 2015 by Delphix. All rights reserved.
+# Copyright (c) 2015, 2018 by Delphix. All rights reserved.
 #
 
 . $STF_SUITE/tests/functional/rsend/rsend.kshlib
@@ -46,7 +46,7 @@ log_must zfs create -o compress=lz4 $sendfs
 log_must zfs create -o compress=lz4 $recvfs
 typeset dir=$(get_prop mountpoint $sendfs)
 # Don't use write_compressible: we want compressible but undedupable data here.
-log_must file_write -o overwrite -f $dir/file -d R -b 4096 -c 1000
+log_must eval "dd if=/dev/urandom bs=1024k count=4 | base64 >$dir/file"
 log_must zfs snapshot $sendfs@snap0
 log_must eval "zfs send -D -c $sendfs@snap0 >$stream0"