diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 52d093d0d0..f145c2ac0b 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -845,6 +845,7 @@ mymain(void)
 # define DO_TEST_CAPS_LATEST_PARSE_ERROR(name) \
     DO_TEST_CAPS_ARCH_LATEST_FULL(name, "x86_64", FLAG_EXPECT_PARSE_ERROR, 0)
 
+
 # define DO_TEST_FULL(name, ...) \
     do { \
         static struct testInfo info = { \
@@ -860,6 +861,9 @@ mymain(void)
         virObjectUnref(info.qemuCaps); \
     } while (0)
 
+/* All the following macros require an explicit QEMU_CAPS_* list
+ * at the end of the argument list, or the NONE placeholder.
+ * */
 # define DO_TEST(name, ...) \
     DO_TEST_FULL(name, \
                  ARG_QEMU_CAPS, __VA_ARGS__)