diff --git a/pkgs/racket-test-core/tests/racket/fasl.rktl b/pkgs/racket-test-core/tests/racket/fasl.rktl
index 5bfc359ee1..6e243516a3 100644
--- a/pkgs/racket-test-core/tests/racket/fasl.rktl
+++ b/pkgs/racket-test-core/tests/racket/fasl.rktl
@@ -73,6 +73,13 @@
 (test #f eq? #rx#"hello" (fasl->s-exp (s-exp->fasl #rx#"hello") #:datum-intern? #f))
 (test #f eq? #px#"hello" (fasl->s-exp (s-exp->fasl #px#"hello") #:datum-intern? #f))
 
+(let* ([r1 #rx"[/\u5C][. ]+ap"]
+       [r2 #px"[/\u5C][. ]+ap"]
+       [r3 #px#"[\\][. ]+ap*"])
+  (test #t equal? r1 (fasl->s-exp (s-exp->fasl r1) #:datum-intern? #f))
+  (test #t equal? r2 (fasl->s-exp (s-exp->fasl r2) #:datum-intern? #f))
+  (test #t equal? r3 (fasl->s-exp (s-exp->fasl r3) #:datum-intern? #f)))
+
 (define (check-hash make-hash hash)
   (let ([mut (make-hash)]
         [immut (hash 'one 2 'three 4)])
diff --git a/racket/collects/racket/fasl.rkt b/racket/collects/racket/fasl.rkt
index b9b67e94bf..9073dac863 100644
--- a/racket/collects/racket/fasl.rkt
+++ b/racket/collects/racket/fasl.rkt
@@ -1,13 +1,24 @@
 #lang racket/base
 (require (for-syntax racket/base)
          "private/truncate-path.rkt"
-         "private/relative-path.rkt")
+         "private/relative-path.rkt"
+         (rename-in racket/base
+                    [write-byte r:write-byte]
+                    [write-bytes r:write-bytes]))
 
 (provide s-exp->fasl
          fasl->s-exp)
 
 ;; ----------------------------------------
 
+;; These wrappers are to make it harder to misuse write-byte(s)
+;; (e.g. calling without the port)
+(define (write-byte byte out)
+  (r:write-byte byte out))
+
+(define (write-bytes bstr out [start-pos 0] [end-pos (bytes-length bstr)])
+  (r:write-bytes bstr out start-pos end-pos))
+
 (define-for-syntax constants (make-hasheq))
 
 (define-syntax (define-constants stx)
@@ -288,10 +299,10 @@
            (write-fasl-integer (hash-count v) o)
            (hash-for-each v (lambda (k v) (loop k) (loop v)) #t)]
           [(regexp? v)
-           (write-byte (if (pregexp? v) fasl-pregexp-type fasl-regexp-type))
+           (write-byte (if (pregexp? v) fasl-pregexp-type fasl-regexp-type) o)
            (write-fasl-string (object-name v) o)]
           [(byte-regexp? v)
-           (write-byte (if (byte-pregexp? v) fasl-byte-pregexp-type fasl-byte-regexp-type))
+           (write-byte (if (byte-pregexp? v) fasl-byte-pregexp-type fasl-byte-regexp-type) o)
            (write-fasl-bytes (object-name v) o)]
           [else
            (raise-arguments-error 'fasl-write