diff --git a/tests/sys/capsicum/Makefile b/tests/sys/capsicum/Makefile
index 6d37cfa0805..fd8dcb29d65 100644
--- a/tests/sys/capsicum/Makefile
+++ b/tests/sys/capsicum/Makefile
@@ -13,6 +13,10 @@ CFLAGS+=	-I${SRCTOP}/tests
 
 GTESTS+=	capsicum-test
 GTESTS_WRAPPER_SH.capsicum-test=	functional
+# This test script runs the same test suite twice, once as root and once as an
+# unprivileged user.  Serialize them since some tests access global namespaces,
+# e.g., mqueuefs, and can trample on each other.
+TEST_METADATA.functional+=	is_exclusive="true"
 
 SRCS.capsicum-test+=	\
 	capsicum-test-main.cc \