diff --git a/tests/sys/acl/Makefile b/tests/sys/acl/Makefile
index abc505efe90..0f2bc98b787 100644
--- a/tests/sys/acl/Makefile
+++ b/tests/sys/acl/Makefile
@@ -23,7 +23,9 @@ TAP_TESTS_SH+=	03
 TAP_TESTS_SH+=	04
 
 .for t in ${TAP_TESTS_SH}
-TEST_METADATA.$t+=	required_user="root"
+# Tests hard-code a ZFS pool name of "acltools" and so cannot run in parallel.
+TEST_METADATA.$t+=	required_user="root" \
+			is_exclusive=true
 .endfor
 
 _ACL_PROGS=		getfacl setfacl