diff --git a/racket/src/io/port/bytes-input.rkt b/racket/src/io/port/bytes-input.rkt
index 96832b1d8b..b9bfe82c44 100644
--- a/racket/src/io/port/bytes-input.rkt
+++ b/racket/src/io/port/bytes-input.rkt
@@ -18,7 +18,9 @@
          peek-bytes!
          peek-bytes-avail!
          peek-bytes-avail!*
-         peek-bytes-avail!/enable-break)
+         peek-bytes-avail!/enable-break
+
+         do-read-byte/core-port)
 
 (module+ internal
   (provide do-read-bytes!))
@@ -49,10 +51,13 @@
 (define/who (read-byte [orig-in (current-input-port)])
   (check who input-port? orig-in)
   (let ([in (->core-input-port orig-in)])
-    (define read-byte (core-input-port-read-byte in))
-    (cond
-      [read-byte (do-read-byte who read-byte in)]
-      [else (read-byte-via-bytes in #:special-ok? #f)])))
+    (do-read-byte/core-port who in)))
+
+(define (do-read-byte/core-port who in)
+  (define read-byte (core-input-port-read-byte in))
+  (cond
+    [read-byte (do-read-byte who read-byte in)]
+    [else (read-byte-via-bytes in #:special-ok? #f)]))
 
 (define/who (read-bytes amt [in (current-input-port)])
   (check who exact-nonnegative-integer? amt)
diff --git a/racket/src/io/port/line-input.rkt b/racket/src/io/port/line-input.rkt
index ad9105445b..aeb5319651 100644
--- a/racket/src/io/port/line-input.rkt
+++ b/racket/src/io/port/line-input.rkt
@@ -1,5 +1,6 @@
 #lang racket/base
-(require "../common/check.rkt"
+(require racket/fixnum
+         "../common/check.rkt"
          "input-port.rkt"
          "bytes-input.rkt"
          "string-input.rkt"
@@ -16,23 +17,24 @@
 (define-syntax-rule (define-read-line read-line
                       make-string string-length string-set! 
                       string-copy! substring
-                      read-char peek-char
+                      do-read-char peek-char
                       as-char)
-  (define/who (read-line [in (current-input-port)] [mode 'linefeed])
-    (check who input-port? in)
+  (define/who (read-line [orig-in (current-input-port)] [mode 'linefeed])
+    (check who input-port? orig-in)
     (check who ok-mode? #:contract ok-mode-str mode)
+    (define in (->core-input-port orig-in))
     (maybe-flush-stdout in)
     (define cr? (memq mode '(return any any-one)))
     (define lf? (memq mode '(linefeed any any-one)))
     (define crlf? (memq mode '(return-linefeed any)))
     (let loop ([str (make-string 32)] [pos 0])
-      (define ch (read-char in))
+      (define ch (do-read-char 'read-line in))
       (define (keep-char)
-        (if (pos . < . (string-length str))
+        (if (pos . fx< . (string-length str))
             (begin
               (string-set! str pos ch)
               (loop str (add1 pos)))
-            (let ([new-str (make-string (* (string-length str) 2))])
+            (let ([new-str (make-string (fx* (string-length str) 2))])
               (string-copy! new-str 0 str 0)
               (string-set! new-str pos ch)
               (loop new-str (add1 pos)))))
@@ -46,7 +48,7 @@
         (cond
          [(and crlf?
                (eqv? (peek-char in) (as-char #\linefeed)))
-          (read-char in)
+          (do-read-char 'read-line in)
           (substring str 0 pos)]
          [cr?
           (substring str 0 pos)]
@@ -59,11 +61,11 @@
 (define-read-line read-line
   make-string string-length string-set! 
   string-copy! substring
-  read-char peek-char
+  do-read-char/core-port peek-char
   values)
 
  (define-read-line read-bytes-line
    make-bytes bytes-length bytes-set! 
    bytes-copy! subbytes
-   read-byte peek-byte
+   do-read-byte/core-port peek-byte
    char->integer)
diff --git a/racket/src/io/port/string-input.rkt b/racket/src/io/port/string-input.rkt
index 671b784a54..b9d4015582 100644
--- a/racket/src/io/port/string-input.rkt
+++ b/racket/src/io/port/string-input.rkt
@@ -21,6 +21,7 @@
          peek-string!
 
          do-read-char
+         do-read-char/core-port
          do-peek-char)
 
 ;; ----------------------------------------
@@ -265,19 +266,21 @@
 
 ;; If `special-ok?`, can return a special-value procedure
 (define (do-read-char who in #:special-ok? [special-ok? #f])
-  (check who input-port? in)
   (let ([in (->core-input-port in)])
-    (define read-byte (core-input-port-read-byte in))
-    (cond
-      [(not read-byte)
-       (define str (make-string 1))
-       (define-values (v used-bytes) (read-some-chars! who in str 0 1 #:special-ok? special-ok?))
-       (if (eq? v 1)
-           (string-ref str 0)
-           v)]
-      [else
-       ;; Byte-level shortcut is available, so try it as a char shortcut
-       (read-char-via-read-byte who in read-byte #:special-ok? special-ok?)])))
+    (do-read-char/core-port who in #:special-ok? special-ok?)))
+
+(define (do-read-char/core-port who in #:special-ok? [special-ok? #f])
+  (define read-byte (core-input-port-read-byte in))
+  (cond
+    [(not read-byte)
+     (define str (make-string 1))
+     (define-values (v used-bytes) (read-some-chars! who in str 0 1 #:special-ok? special-ok?))
+     (if (eq? v 1)
+         (string-ref str 0)
+         v)]
+    [else
+     ;; Byte-level shortcut is available, so try it as a char shortcut
+     (read-char-via-read-byte who in read-byte #:special-ok? special-ok?)]))
 
 (define/who (read-char [in (current-input-port)])
   (check who input-port? in)