diff --git a/scripts/zfs-tests.sh b/scripts/zfs-tests.sh
index a058eb9c59..94c6ab0b11 100755
--- a/scripts/zfs-tests.sh
+++ b/scripts/zfs-tests.sh
@@ -333,7 +333,7 @@ OPTIONS:
 	-m          Enable kmemleak reporting (Linux only)
 	-n NFSFILE  Use the nfsfile to determine the NFS configuration
 	-I NUM      Number of iterations
-	-d DIR      Use DIR for files and loopback devices
+	-d DIR      Use world-writable DIR for files and loopback devices
 	-s SIZE     Use vdevs of SIZE (default: 4G)
 	-r RUNFILES Run tests in RUNFILES (default: ${DEFAULT_RUNFILES})
 	-t PATH     Run single test at PATH relative to test suite
diff --git a/tests/README.md b/tests/README.md
index a01ffbe12c..774bcc4171 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -88,6 +88,7 @@ The following zfs-tests.sh options are supported:
 
     -d DIR      Create sparse files for vdevs in the DIR directory.  By
                 default these files are created under /var/tmp/.
+                This directory must be world-writable.
 
     -s SIZE     Use vdevs of SIZE (default: 4G)