diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index 62097f1e..e6693076 100755
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -1159,6 +1159,7 @@ enum sexp_context_globals {
   SEXP_G_ABI_ERROR,             /* incompatible ABI loading library */
   SEXP_G_OPTIMIZATIONS,
   SEXP_G_SIGNAL_HANDLERS,
+  SEXP_G_FILE_DESCRIPTORS,
   SEXP_G_META_ENV,
   SEXP_G_MODULE_PATH,
   SEXP_G_QUOTE_SYMBOL,
@@ -1306,7 +1307,7 @@ SEXP_API sexp sexp_read_from_string (sexp ctx, const char *str, sexp_sint_t len)
 SEXP_API sexp sexp_write_to_string (sexp ctx, sexp obj);
 SEXP_API sexp sexp_write_simple_object (sexp ctx, sexp self, sexp_sint_t n, sexp obj, sexp writer, sexp out);
 SEXP_API sexp sexp_finalize_port (sexp ctx, sexp self, sexp_sint_t n, sexp port);
-SEXP_API sexp sexp_make_fileno (sexp ctx, int fd, int no_closep);
+SEXP_API sexp sexp_make_fileno_op (sexp ctx, sexp self, sexp_sint_t n, sexp fd, sexp no_closep);
 SEXP_API sexp sexp_make_input_port (sexp ctx, FILE* in, sexp name);
 SEXP_API sexp sexp_make_output_port (sexp ctx, FILE* out, sexp name);
 SEXP_API sexp sexp_open_input_file_descriptor (sexp ctx, sexp self, sexp_sint_t n, sexp fileno, sexp socketp);
@@ -1444,6 +1445,7 @@ SEXP_API sexp sexp_finalize_c_type (sexp ctx, sexp self, sexp_sint_t n, sexp obj
 #define sexp_make_getter(ctx, a, b, c) sexp_make_getter_op(ctx, NULL, 3, a, b, c)
 #define sexp_make_setter(ctx, a, b, c) sexp_make_setter_op(ctx, NULL, 3, a, b, c)
 #define sexp_lookup_type(ctx, name, id) sexp_lookup_type_op(ctx, NULL, 2, name, id)
+#define sexp_make_fileno(ctx, fd, no_closep) sexp_make_fileno_op(ctx, NULL, 2, fd, no_closep)
 
 enum sexp_opcode_names {
   SEXP_OP_NOOP,
diff --git a/lib/chibi/accept.c b/lib/chibi/accept.c
index d6970e57..a93e613c 100644
--- a/lib/chibi/accept.c
+++ b/lib/chibi/accept.c
@@ -19,7 +19,7 @@ sexp sexp_accept (sexp ctx, sexp self, int sock, struct sockaddr* addr, socklen_
     }
   }
 #endif
-  return sexp_make_fileno(ctx, res, 0);
+  return sexp_make_fileno(ctx, sexp_make_fixnum(res), SEXP_FALSE);
 }
 
 /* If we're listening on a socket from Scheme, we most likely want it */
diff --git a/lib/chibi/process.scm b/lib/chibi/process.scm
index 040dbf21..b4221824 100644
--- a/lib/chibi/process.scm
+++ b/lib/chibi/process.scm
@@ -49,23 +49,6 @@
      (else
       (waitpid pid 0)))))
 
-(define (string-char-index str c . o)
-  (let ((start (if (pair? o) (car o) 0))
-        (end (if (and (pair? o) (pair? (cdr o))) (cadr o) (string-length str))))
-    (let lp ((i start))
-      (cond
-       ((= i end) #f)
-       ((eq? c (string-ref str i)) i)
-       (else (lp (+ i 1)))))))
-
-(define (string-split str ch)
-  (let ((len (string-length str)))
-    (let lp ((i 0) (res '()))
-      (let ((j (string-char-index str ch i)))
-        (if j
-            (lp (+ j 1) (cons (substring str i j) res))
-            (reverse (cons (substring str i len) res)))))))
-
 (define (call-with-process-io command proc)
   (let ((command-ls (if (string? command) (string-split command) command))
         (in-pipe (open-pipe))
diff --git a/lib/chibi/process.sld b/lib/chibi/process.sld
index 641a4e56..03364555 100644
--- a/lib/chibi/process.sld
+++ b/lib/chibi/process.sld
@@ -16,7 +16,7 @@
           signal/tty-output wait/no-hang
           call-with-process-io
           process->string process->string-list process->output+error)
-  (import (scheme) (chibi io) (chibi filesystem))
+  (import (scheme) (chibi io) (chibi strings) (chibi filesystem))
   (cond-expand (threads (import (srfi 18))) (else #f))
   (include-shared "process")
   (include "process.scm"))
diff --git a/sexp.c b/sexp.c
index 823eb105..ae681b1c 100644
--- a/sexp.c
+++ b/sexp.c
@@ -1553,13 +1553,14 @@ sexp sexp_open_output_file_descriptor (sexp ctx, sexp self, sexp_sint_t n, sexp
 
 #endif  /* ! SEXP_USE_STRING_STREAMS */
 
-sexp sexp_make_fileno (sexp ctx, int fd, int no_closep) {
+sexp sexp_make_fileno_op (sexp ctx, sexp self, sexp_sint_t n, sexp fd, sexp no_closep) {
   sexp res;
-  if (fd < 0) return SEXP_FALSE;
+  sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, fd);
+  if (sexp_unbox_fixnum(fd) < 0) return SEXP_FALSE;
   res = sexp_alloc_type(ctx, fileno, SEXP_FILENO);
   if (!sexp_exceptionp(res)) {
-    sexp_fileno_fd(res) = fd;
-    sexp_fileno_no_closep(res) = no_closep;
+    sexp_fileno_fd(res) = sexp_unbox_fixnum(fd);
+    sexp_fileno_no_closep(res) = sexp_truep(no_closep);
   }
   return res;
 }
diff --git a/tools/chibi-ffi b/tools/chibi-ffi
index ebd356b6..ac6953cf 100755
--- a/tools/chibi-ffi
+++ b/tools/chibi-ffi
@@ -607,7 +607,7 @@
      ((eq? 'input-output-port base)
       (cat "sexp_make_non_null_input_output_port(ctx, " val ", SEXP_FALSE)"))
      ((eq? 'fileno base)
-      (cat "sexp_make_fileno(ctx, " val ", 0)"))
+      (cat "sexp_make_fileno(ctx, sexp_make_fixnum(" val "), SEXP_FALSE)"))
      (else
       (let ((ctype (lookup-type base))
             (void*? (void-pointer-type? type)))
@@ -656,7 +656,8 @@
      ((port-type? base)
       (cat "sexp_port_stream(" val ")"))
      ((eq? base 'fileno)
-      (cat "sexp_fileno_fd(" val ")"))
+      (cat "(sexp_filenop(" val ") ? sexp_fileno_fd(" val ")"
+           " : sexp_unbox_fixnum(" val "))"))
      (else
       (let ((ctype (lookup-type base))
             (void*? (void-pointer-type? type)))
@@ -711,8 +712,10 @@
      ((eq? base 'env-string)
       (cat "(sexp_pairp(" arg ") && sexp_stringp(sexp_car(" arg
            ")) && sexp_stringp(sexp_cdr(" arg ")))"))
+     ((eq? base 'fileno)
+      (cat "(sexp_filenop(" arg ") || sexp_fixnump(" arg "))"))
      ((or (int-type? base) (float-type? base)
-          (string-type? base) (port-type? base) (eq? base 'fileno))
+          (string-type? base) (port-type? base))
       (cat (type-predicate type) "(" arg ")"))
      ((or (lookup-type base) (void-pointer-type? type))
       (cat