diff --git a/doc/guix.texi b/doc/guix.texi
index 2bebeeddf7..004e50c86b 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -6302,7 +6302,12 @@ is interpreted as a partition label name; when it is @code{uuid},
 @code{device} is interpreted as a partition unique identifier (UUID).
 
 UUIDs may be converted from their string representation (as shown by the
-@command{tune2fs -l} command) using the @code{uuid} form, like this:
+@command{tune2fs -l} command) using the @code{uuid} form@footnote{The
+@code{uuid} form expects 16-byte UUIDs as defined in
+@uref{https://tools.ietf.org/html/rfc4122, RFC@tie{}4122}.  This is the
+form of UUID used by the ext2 family of file systems and others, but it
+is different from ``UUIDs'' found in FAT file systems, for instance.},
+like this:
 
 @example
 (file-system