diff --git a/racket/collects/setup/setup-core.rkt b/racket/collects/setup/setup-core.rkt
index 3286341c57..79911df43f 100644
--- a/racket/collects/setup/setup-core.rkt
+++ b/racket/collects/setup/setup-core.rkt
@@ -155,6 +155,11 @@
     (let ([v (getenv "PLT_SETUP_DMS_ARGS")])
       (and v (read (open-input-string v)))))
 
+  ;; Also help to check for leaks: set `PLT_SETUP_LIMIT_CACHE` to
+  ;; avoid caching compile-file information across different collections:
+  (define limit-cross-collection-cache?
+    (getenv "PLT_SETUP_LIMIT_CACHE"))
+
   ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;                   Errors                      ;;
   ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@@ -1069,8 +1074,10 @@
 
   ;; We keep timestamp information for all files that we try to compile.
   ;; That's O(N) for an installation of size N, but the constant is small,
-  ;; and it makes a do-nothing setup complete much faster.
-  (define caching-managed-compile-zo (make-caching-managed-compile-zo))
+  ;; and it makes a do-nothing setup complete much faster. But set the
+  ;; `PLT_SETUP_LIMIT_CACHE` environment variable to disable it.
+  (define caching-managed-compile-zo (and (not limit-cross-collection-cache?)
+                                          (make-caching-managed-compile-zo)))
 
   (define (compile-cc cc gcs has-module-suffix?)
     (parameterize ([current-namespace (make-base-empty-namespace)])
@@ -1090,7 +1097,8 @@
                                   #:verbose (verbose)
                                   #:has-module-suffix? has-module-suffix?
                                   #:omit-root (cc-omit-root cc)
-                                  #:managed-compile-zo caching-managed-compile-zo
+                                  #:managed-compile-zo (or caching-managed-compile-zo
+                                                           (make-caching-managed-compile-zo))
                                   #:skip-path (and (avoid-main-installation) main-collects-dir)
                                   #:skip-doc-sources? (not make-docs?))))))
     (when post-collection-dms-args
diff --git a/racket/src/cs/rumble/memory.ss b/racket/src/cs/rumble/memory.ss
index a8b6854489..6eca4439a0 100644
--- a/racket/src/cs/rumble/memory.ss
+++ b/racket/src/cs/rumble/memory.ss
@@ -286,6 +286,14 @@
      #%procedure?]
     [(eq? 'ephemeron (car args))
      ephemeron-pair?]
+    [(eq? 'bignum (car args))
+     bignum?]
+    [(eq? 'keyword (car args))
+     keyword?]
+    [(eq? 'string (car args))
+     string?]
+    [(eq? 'symbol (car args))
+     symbol?]
     [(eq? '<ffi-lib> (car args))
      ffi-lib?]
     [(eq? '<will-executor> (car args))
diff --git a/racket/src/cs/rumble/prefab.ss b/racket/src/cs/rumble/prefab.ss
index d878e35a04..cdc698a570 100644
--- a/racket/src/cs/rumble/prefab.ss
+++ b/racket/src/cs/rumble/prefab.ss
@@ -303,7 +303,10 @@
       '#()))
 
 (define (encode-prefab-key+count-as-symbol prefab-key+count)
-  (string->symbol (chez:format "~a" prefab-key+count)))
+  ;; The symbol has to be uninterned, because we're going to attach
+  ;; properties to it, and an interned symbol with properties is never
+  ;; reclaimed by the garbage collector
+  (#%gensym (#%format "~s" prefab-key+count)))
 
 (define (immutables->mutables immutables init-count auto-count)
   (vector->immutable-vector
diff --git a/racket/src/cs/rumble/struct.ss b/racket/src/cs/rumble/struct.ss
index af51062ffa..44d04eb8b4 100644
--- a/racket/src/cs/rumble/struct.ss
+++ b/racket/src/cs/rumble/struct.ss
@@ -571,7 +571,7 @@
     (record-type-uid
      (prefab-key+count->rtd (cons prefab-key total*-count)))))
 
-;; A weak, `equal?`-based hash table that maps (cons prefab-key
+;; An emphemeron-weak, `equal?`-based hash table that maps (cons prefab-key
 ;; total-field-count) to rtd. We'll create a table without a lock, and
 ;; we'll use it for all places, which means that we need to use a
 ;; global lock to access the table. Compute a hash code outside the
@@ -581,7 +581,10 @@
 ;; Call with lock:
 (define (prefab-ref prefab-key+count code)
   (and prefabs
-       (weak-hash-ref prefabs prefab-key+count #f code equal?)))
+       (let ([e (weak-hash-ref prefabs prefab-key+count #f code equal?)])
+         (and e
+              (not (eq? (car e) #!bwp))
+              (cdr e)))))
 
 (define (prefab-key+count->rtd prefab-key+count)
   (let ([code (equal-hash-code prefab-key+count)])
@@ -615,7 +618,7 @@
           [else
            (putprop uid 'prefab-key+count prefab-key+count)
            (unless prefabs (set! prefabs (make-weak-hash-with-lock #f)))
-           (weak-hash-set! prefabs prefab-key+count rtd code equal?)
+           (weak-hash-set! prefabs prefab-key+count (ephemeron-cons prefab-key+count rtd) code equal?)
            (unless parent-rtd
              (record-type-equal-procedure rtd default-struct-equal?)
              (record-type-hash-procedure rtd default-struct-hash))