diff --git a/src/libnm-glib-aux/nm-uuid.h b/src/libnm-glib-aux/nm-uuid.h
index 15b03a2d47..f84778998e 100644
--- a/src/libnm-glib-aux/nm-uuid.h
+++ b/src/libnm-glib-aux/nm-uuid.h
@@ -9,6 +9,9 @@ typedef struct _NMUuid {
 
 #define NM_UUID_INIT_ZERO() ((NMUuid){.uuid = {0}})
 
+/* Beware, the 16 macro arguments are two hex-digits, not plain numbers. The macro
+ * will automatically add the "0x". In particular, "09" is not an octal number, it's
+ * 0x09. This oddity is so that the arguments look very much like the UUID in string form. */
 #define NM_UUID_INIT(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15) \
     ((NMUuid){                                                                             \
         .uuid = {(0x##a0),                                                                 \