diff --git a/tests/sys/netpfil/pf/Makefile b/tests/sys/netpfil/pf/Makefile
index 7256602a55a..25029972769 100644
--- a/tests/sys/netpfil/pf/Makefile
+++ b/tests/sys/netpfil/pf/Makefile
@@ -38,6 +38,9 @@ ATF_TESTS_SH+=	altq \
 		table \
 		tos
 
+# Tests reuse jail names and so cannot run in parallel.
+TEST_METADATA+=	is_exclusive=true
+
 ${PACKAGE}FILES+=	CVE-2019-5597.py \
 			CVE-2019-5598.py \
 			daytime_inetd.conf \