diff --git a/lib/libcasper/services/cap_sysctl/tests/Makefile b/lib/libcasper/services/cap_sysctl/tests/Makefile
index d0d9f9bd7a0d..ec7439351c66 100644
--- a/lib/libcasper/services/cap_sysctl/tests/Makefile
+++ b/lib/libcasper/services/cap_sysctl/tests/Makefile
@@ -11,6 +11,9 @@ CFLAGS+=-DWITH_CASPER
 .endif
 LIBADD+=	nv
 
-TEST_METADATA.sysctl_test+=	required_user="root"
+# cap_sysctl tests modify global sysctl values and read them back, so
+# cannot be run in parallel.
+TEST_METADATA.sysctl_test+=	required_user="root" \
+				is_exclusive=true
 
 .include <bsd.test.mk>