diff --git a/pkgs/racket-test-core/tests/racket/prompt.rktl b/pkgs/racket-test-core/tests/racket/prompt.rktl
index 542262ea45..5fa25de054 100644
--- a/pkgs/racket-test-core/tests/racket/prompt.rktl
+++ b/pkgs/racket-test-core/tests/racket/prompt.rktl
@@ -588,4 +588,76 @@
 
 ;;----------------------------------------
 
+(let* ([t (make-continuation-prompt-tag 't)])
+  (test #t continuation-prompt-available? t
+        (call-with-continuation-prompt
+         (lambda ()
+           (call/cc (lambda (k) k)
+                    t))
+         t))
+  (test #f continuation-prompt-available? t
+        (call-with-continuation-prompt
+         (lambda ()
+           (call-with-composable-continuation
+            (lambda (k) k)
+            t))
+         t))
+  (let ([k (call-with-continuation-prompt
+            (lambda ()
+              ((call-with-composable-continuation
+                (lambda (k) (lambda () k))
+                t)))
+            t)])
+    (test #f continuation-prompt-available? t k)
+    (test #f values
+          (k (lambda ()
+               (continuation-prompt-available? t))))
+    (test #f continuation-prompt-available? (default-continuation-prompt-tag) k))
+  (let ([k (call-with-continuation-prompt
+            (lambda ()
+              ((call-with-current-continuation
+                (lambda (k) (lambda () k))
+                t)))
+            t)])
+    (test #t continuation-prompt-available? t k)
+    (test #t values
+          (call-with-continuation-prompt
+            (lambda ()
+              (k (lambda ()
+                   (continuation-prompt-available? t))))
+            t))
+    (test #f continuation-prompt-available? (default-continuation-prompt-tag) k))
+  (test #t continuation-prompt-available? t
+        (call-with-continuation-prompt
+         (lambda ()
+           (call-with-continuation-prompt
+            (lambda ()
+              (call-with-current-continuation
+               (lambda (k) k)))
+            t))))
+  (test #t continuation-prompt-available? t
+        (call-with-continuation-prompt
+         (lambda ()
+           (call-with-continuation-prompt
+            (lambda ()
+              (call-with-composable-continuation
+               (lambda (k) k)))
+            t))))
+  (test #t 'continuation-prompt-available?
+        (call-with-continuation-prompt
+         (lambda ()
+           (call-with-escape-continuation
+            (lambda (k) (continuation-prompt-available? t k))))
+         t))
+  (err/rt-test (continuation-prompt-available?
+                t
+                (call-with-continuation-prompt
+                 (lambda ()
+                   (call-with-escape-continuation
+                    (lambda (k) k)))
+                 t))
+               exn:fail:contract:continuation?))
+
+;;----------------------------------------
+
 (report-errs)
diff --git a/racket/src/cs/rumble/control.ss b/racket/src/cs/rumble/control.ss
index 6f2dba1208..596f8ae08e 100644
--- a/racket/src/cs/rumble/control.ss
+++ b/racket/src/cs/rumble/control.ss
@@ -142,15 +142,31 @@
 ;; thunks:
 (define break-enabled-key '#{break-enabled n1kcvqw4c9hh8t3fi3659ci94-2})
 
-(define/who (continuation-prompt-available? tag)
-  (check who continuation-prompt-tag? tag)
+(define/who continuation-prompt-available?
+  (case-lambda
+   [(tag)
+    (check who continuation-prompt-tag? tag)
+    (is-continuation-prompt-available? tag (current-metacontinuation))]
+   [(tag k)
+    (check who continuation-prompt-tag? tag)
+    (check who continuation? k)
+    (when (escape-continuation? k)
+      (unless (is-continuation-prompt-available? (escape-continuation-tag k) #f)
+        (raise-continuation-error who
+                                  "escape continuation not in the current thread's continuation")))
+    (or (is-continuation-prompt-available? tag (continuation-mc k))
+        (and (non-composable-continuation? k)
+             (eq? (strip-impersonator tag) (strip-impersonator (full-continuation-tag k)))))]))
+
+(define (is-continuation-prompt-available? tag mc)
   (maybe-future-barricade tag)
   (let ([tag (strip-impersonator tag)])
-    (or (eq? tag the-default-continuation-prompt-tag)
-        (eq? tag the-root-continuation-prompt-tag)
+    (or (and (not mc)
+             (or (eq? tag the-default-continuation-prompt-tag)
+                 (eq? tag the-root-continuation-prompt-tag)))
         ;; Looks through metacontinuation cache, but cache a search result
         ;; half-way up if the chain is deep enough
-        (let ([mc (current-metacontinuation)])
+        (let ([mc (or mc (current-metacontinuation))])
           (let loop ([mc mc] [slow-mc mc] [slow-step? #f] [steps 0])
             (cond
              [(null? mc)
@@ -426,7 +442,7 @@
        (do-abort-current-continuation who tag args #t)))]))
 
 (define (check-prompt-still-available who tag)
-  (unless (continuation-prompt-available? tag)
+  (unless (is-continuation-prompt-available? tag #f)
     (end-uninterrupted 'escape-fail)
     (raise-continuation-error who
                               (string-append
@@ -455,8 +471,8 @@
 ;; ----------------------------------------
 ;; Capturing and applying continuations
 
-(define-record continuation ())
-(define-record full-continuation continuation (k winders mark-stack mark-splice mc tag))
+(define-record continuation (mc))
+(define-record full-continuation continuation (k winders mark-stack mark-splice tag))
 (define-record composable-continuation full-continuation (wind?))
 (define-record non-composable-continuation full-continuation ())
 (define-record escape-continuation continuation (tag))
@@ -474,11 +490,11 @@
         (|#%app|
          proc
          (make-non-composable-continuation
+          (extract-metacontinuation who (strip-impersonator tag) #t)
           k
           (current-winders)
           (current-mark-stack)
           (current-mark-splice)
-          (extract-metacontinuation who (strip-impersonator tag) #t)
           tag))))]))
 
 (define/who call-with-composable-continuation
@@ -496,11 +512,11 @@
      (|#%app|
       p
       (make-composable-continuation
+       (extract-metacontinuation 'call-with-composable-continuation (strip-impersonator tag) #f)
        k
        (current-winders)
        (current-mark-stack)
        (current-mark-splice)
-       (extract-metacontinuation 'call-with-composable-continuation (strip-impersonator tag) #f)
        tag
        wind?)))))
 
@@ -512,7 +528,7 @@
   (let ([tag (make-continuation-prompt-tag)])
     (call-with-continuation-prompt
      (lambda ()
-       (|#%app| p (make-escape-continuation tag)))
+       (|#%app| p (make-escape-continuation (current-metacontinuation) tag)))
      tag
      values)))
 
@@ -538,7 +554,7 @@
      ;; empty continuation, so we can "replace" that
      ;; with the composable one:
      (cond
-      [(and (null? (full-continuation-mc c))
+      [(and (null? (continuation-mc c))
             (null? (full-continuation-winders c))
             (eq? (current-mark-splice) (full-continuation-mark-splice c))
             (let ([marks (continuation-next-attachments (full-continuation-k c))])
@@ -551,13 +567,13 @@
       [(not (composable-continuation-wind? c))
        (apply-immediate-continuation/no-wind c args)]
       [else
-       (apply-immediate-continuation c (reverse (full-continuation-mc c)) args)]))))
+       (apply-immediate-continuation c (reverse (continuation-mc c)) args)]))))
 
 ;; Applying an escape continuation calls this internal function:
 (define (apply-escape-continuation c args)
   (start-uninterrupted 'continue)
   (let ([tag (escape-continuation-tag c)])
-    (unless (continuation-prompt-available? tag)
+    (unless (is-continuation-prompt-available? tag #f)
       (end-uninterrupted 'escape-fail)
       (raise-continuation-error '|continuation application|
                                 "attempt to jump into an escape continuation"))
@@ -571,7 +587,7 @@
 (define (apply-non-composable-continuation* c args)
   (assert-in-uninterrupted)
   (let ([mc (current-metacontinuation)]
-        [c-mc (full-continuation-mc c)]
+        [c-mc (continuation-mc c)]
         [tag (full-continuation-tag c)])
     (cond
      [(and (null? c-mc)
@@ -647,7 +663,7 @@
 ;; Like `apply-immediate-continuation`, but don't run winders
 (define (apply-immediate-continuation/no-wind c args)
   (current-metacontinuation (append
-                             (map metacontinuation-frame-clear-cache (full-continuation-mc c))
+                             (map metacontinuation-frame-clear-cache (continuation-mc c))
                              (current-metacontinuation)))
   (current-winders (full-continuation-winders c))
   (current-mark-splice (full-continuation-mark-splice c))
@@ -769,7 +785,7 @@
                                      (eq? a-tag the-barrier-prompt-tag))))]))]))))
 
 (define (check-prompt-tag-available who tag)
-  (unless (continuation-prompt-available? tag)
+  (unless (is-continuation-prompt-available? tag #f)
     (raise-no-prompt-tag who tag)))
 
 (define (raise-no-prompt-tag who tag)
@@ -1487,11 +1503,11 @@
                 orig-tag)
            (get-mark-chain (full-continuation-mark-stack k)
                            (full-continuation-mark-splice k)
-                           (full-continuation-mc k)))
+                           (continuation-mc k)))
           (cons (continuation->trace (full-continuation-k k))
-                (get-metacontinuation-traces (full-continuation-mc k))))]
+                (get-metacontinuation-traces (continuation-mc k))))]
         [(escape-continuation? k)
-         (unless (continuation-prompt-available? (escape-continuation-tag k))
+         (unless (is-continuation-prompt-available? (escape-continuation-tag k) #f)
            (raise-continuation-error '|continuation application|
                                      "escape continuation not in the current continuation"))
          (make-continuation-mark-set
diff --git a/racket/src/racket/src/fun.c b/racket/src/racket/src/fun.c
index 44aea0a3a8..f590d9f88a 100644
--- a/racket/src/racket/src/fun.c
+++ b/racket/src/racket/src/fun.c
@@ -7642,7 +7642,8 @@ static Scheme_Object *continuation_marks(Scheme_Thread *p,
                                          Scheme_Meta_Continuation *mc,
                                          Scheme_Object *prompt_tag,
                                          char *who,
-					 int just_chain)
+					 int just_chain,
+                                         int use_boundary_prompt)
      /* cont => p is not used */
 {
   Scheme_Cont *cont = (Scheme_Cont *)_cont, *top_cont;
@@ -7656,7 +7657,9 @@ static Scheme_Object *continuation_marks(Scheme_Thread *p,
   if (SAME_OBJ(prompt_tag, scheme_root_prompt_tag))
     prompt_tag = NULL;
 
-  if (cont && SAME_OBJ(cont->prompt_tag, prompt_tag))
+  if (cont
+      && (use_boundary_prompt || !cont->composable)
+      && SAME_OBJ(cont->prompt_tag, prompt_tag))
     found_tag = 1;
   if (!prompt_tag)
     found_tag = 1;
@@ -7898,6 +7901,9 @@ static Scheme_Object *continuation_marks(Scheme_Thread *p,
                        "%s: no corresponding prompt in the continuation\n"
                        "  tag: %V",
                        who, prompt_tag);
+    } else if (!use_boundary_prompt) {
+      /* Don't treat default tag as found */
+      return NULL;
     }
   }
 
@@ -7950,7 +7956,7 @@ Scheme_Object *scheme_current_continuation_marks(Scheme_Object *prompt_tag)
   return continuation_marks(scheme_current_thread, NULL, NULL, NULL, 
                             prompt_tag ? prompt_tag : scheme_default_prompt_tag,
                             "continuation-marks",
-                            0);
+                            0, 1);
 }
 
 Scheme_Object *scheme_all_current_continuation_marks()
@@ -7958,7 +7964,7 @@ Scheme_Object *scheme_all_current_continuation_marks()
   return continuation_marks(scheme_current_thread, NULL, NULL, NULL, 
                             NULL,
                             "continuation-marks",
-                            0);
+                            0, 1);
 }
 
 static Scheme_Object *
@@ -8027,7 +8033,7 @@ cont_marks(int argc, Scheme_Object *argv[])
       mc = scheme_get_meta_continuation(argv[0]);
 
       return continuation_marks(scheme_current_thread, NULL, argv[0], mc, prompt_tag, 
-                                "continuation-marks", 0);
+                                "continuation-marks", 0, 1);
     }
   } else if (SCHEME_THREADP(argv[0])) {
     Scheme_Thread *t = (Scheme_Thread *)argv[0];
@@ -8062,7 +8068,7 @@ cont_marks(int argc, Scheme_Object *argv[])
     }
   } else {
     return continuation_marks(NULL, argv[0], NULL, NULL, prompt_tag, 
-                              "continuation-marks", 0);
+                              "continuation-marks", 0, 1);
   }
 }
 
@@ -8881,11 +8887,11 @@ static Scheme_Object *continuation_prompt_available(int argc, Scheme_Object *arg
         mc = scheme_get_meta_continuation(argv[1]);
         
         if (continuation_marks(scheme_current_thread, NULL, argv[1], mc, prompt_tag, 
-                               NULL, 0))
+                               NULL, 0, 0))
           return scheme_true;
       }
     } else if (SCHEME_CONTP(argv[1])) {
-      if (continuation_marks(NULL, argv[1], NULL, NULL, prompt_tag, NULL, 0))
+      if (continuation_marks(NULL, argv[1], NULL, NULL, prompt_tag, NULL, 0, 0))
         return scheme_true;
     } else {
       scheme_wrong_contract("continuation-prompt-available?", "continuation?",