diff --git a/lib/chibi/io.sld b/lib/chibi/io.sld
index b8d4da82..1ee8ccbb 100644
--- a/lib/chibi/io.sld
+++ b/lib/chibi/io.sld
@@ -2,7 +2,8 @@
 (define-library (chibi io)
   (export read-string read-string! read-line write-line
           port-fold port-fold-right port-map
-          port->list port->string-list port->sexp-list port->string
+          port->list port->string-list port->sexp-list
+          port->string port->bytevector
           file-position set-file-position! seek/set seek/cur seek/end
           make-custom-input-port make-custom-output-port
           make-custom-binary-input-port make-custom-binary-output-port
diff --git a/lib/chibi/io/io.scm b/lib/chibi/io/io.scm
index 7100e235..abe5ca90 100644
--- a/lib/chibi/io/io.scm
+++ b/lib/chibi/io/io.scm
@@ -225,6 +225,12 @@
 (define (port->string in)
   (string-concatenate (port->list (lambda (in) (read-string 1024 in)) in)))
 
+(define (port->bytevector in)
+  (let ((out (open-output-bytevector)))
+    (do ((c (read-u8 in) (read-u8 in)))
+        ((eof-object? c) (get-output-bytevector out))
+      (write-u8 c out))))
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; custom port utilities