diff --git a/collects/racket/sandbox.rkt b/collects/racket/sandbox.rkt
index 0a7979de20..5cad282900 100644
--- a/collects/racket/sandbox.rkt
+++ b/collects/racket/sandbox.rkt
@@ -32,6 +32,7 @@
          evaluator-alive?
          kill-evaluator
          break-evaluator
+         get-user-custodian
          set-eval-limits
          set-eval-handler
          put-input
@@ -621,6 +622,7 @@
 (define-evaluator-messenger evaluator-alive? 'alive?)
 (define-evaluator-messenger kill-evaluator 'kill)
 (define-evaluator-messenger break-evaluator 'break)
+(define-evaluator-messenger get-user-custodian 'user-cust)
 (define-evaluator-messenger (set-eval-limits secs mb) 'limits)
 (define-evaluator-messenger (set-eval-handler handler) 'handler)
 (define-evaluator-messenger (put-input . xs) 'input)
@@ -819,6 +821,7 @@
           [(alive?)  (and user-thread (not (thread-dead? user-thread)))]
           [(kill)    (terminate+kill! 'evaluator-killed #f)]
           [(break)   (user-break)]
+          [(user-cust) user-cust]
           [(limits)  (set! limits (evaluator-message-args expr))]
           [(handler) (set! eval-handler (car (evaluator-message-args expr)))]
           [(input)   (apply input-putter (evaluator-message-args expr))]
diff --git a/collects/scribblings/reference/sandbox.scrbl b/collects/scribblings/reference/sandbox.scrbl
index 55f926f5c5..dfdee6878f 100644
--- a/collects/scribblings/reference/sandbox.scrbl
+++ b/collects/scribblings/reference/sandbox.scrbl
@@ -730,6 +730,19 @@ Ctrl-C was typed when the evaluator is currently executing, which
 propagates the break to the evaluator's context.}
 
 
+@defproc[(get-user-custodian [evaluator (any/c . -> . any)]) void?]{
+
+Retrieves the @racket[evaluator]'s toplevel custodian.  This returns a
+value that is different from @racket[(evaluator '(current-custodian))]
+or @racket[call-in-sandbox-context evaluator current-custodian] --- each
+sandbox interaction is wrapped in its own custodian, which is what these
+would return.
+
+(One use for this custodian is with @racket[current-memory-use], where
+the per-interaction sub-custodians will not be charged with the memory
+for the whole sandbox.)}
+
+
 @defproc[(set-eval-limits [evaluator (any/c . -> . any)]
                           [secs (or/c exact-nonnegative-integer? #f)]
                           [mb (or/c exact-nonnegative-integer? #f)])