diff --git a/pkgs/racket-pkgs/racket-doc/scribblings/reference/plumbers.scrbl b/pkgs/racket-pkgs/racket-doc/scribblings/reference/plumbers.scrbl
index 2f50772843..92afd56bc5 100644
--- a/pkgs/racket-pkgs/racket-doc/scribblings/reference/plumbers.scrbl
+++ b/pkgs/racket-pkgs/racket-doc/scribblings/reference/plumbers.scrbl
@@ -6,7 +6,9 @@
 A @deftech{plumber} supports @deftech{flush callbacks}, which are
 normally triggered just before a Racket process or @tech{place} exits.
 For example, a @tech{flush callback} might flush an output port's
-buffer.
+buffer.@margin-note{@tech{Flush callbacks} are roughly analogous to the standard C
+library's @as-index{@tt{atexit}}, but flush callback can also be used in other,
+similar scenarios.}
 
 There is no guarantee that a flush callback will be called before a
 process terminates---either because the plumber is not the original