diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index 905fe358..33742a26 100755
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -32,6 +32,7 @@ extern "C" {
 #if SEXP_USE_GREEN_THREADS
 #include <sys/time.h>
 #include <fcntl.h>
+#include <poll.h>
 #endif
 #define sexp_isalpha(x) (isalpha(x))
 #define sexp_isxdigit(x) (isxdigit(x))
@@ -1352,6 +1353,7 @@ SEXP_API sexp sexp_read_complex_tail(sexp ctx, sexp in, sexp res);
 #endif
 SEXP_API sexp sexp_read_raw (sexp ctx, sexp in);
 SEXP_API sexp sexp_read_op (sexp ctx, sexp self, sexp_sint_t n, sexp in);
+SEXP_API sexp sexp_char_ready_p (sexp ctx, sexp self, sexp_sint_t n, sexp in);
 SEXP_API sexp sexp_read_from_string (sexp ctx, const char *str, sexp_sint_t len);
 SEXP_API sexp sexp_read_error (sexp ctx, const char *msg, sexp ir, sexp port);
 SEXP_API sexp sexp_write_to_string (sexp ctx, sexp obj);
diff --git a/lib/init-7.scm b/lib/init-7.scm
index 2c9c315b..d2d50515 100644
--- a/lib/init-7.scm
+++ b/lib/init-7.scm
@@ -498,9 +498,6 @@
 
 (define textual-port? port?)
 
-(define (char-ready? . o)
-  (not (eof-object? (peek-char (if (pair? o) (car o) (current-input-port))))))
-
 (define (call-with-input-string str proc)
   (let* ((in (open-input-string str))
          (res (proc in)))
diff --git a/opcodes.c b/opcodes.c
index 31934921..5af07da6 100644
--- a/opcodes.c
+++ b/opcodes.c
@@ -142,6 +142,7 @@ _OP(SEXP_OPC_IO, SEXP_OP_WRITE_STRING, 2, 3, SEXP_VOID, _I(SEXP_STRING), _I(SEXP
 _OP(SEXP_OPC_IO, SEXP_OP_READ_CHAR, 0, 3, _I(SEXP_CHAR), _I(SEXP_IPORT), SEXP_FALSE, SEXP_FALSE, 0, "read-char", (sexp)"current-input-port", NULL),
 _OP(SEXP_OPC_IO, SEXP_OP_PEEK_CHAR, 0, 3, _I(SEXP_CHAR), _I(SEXP_IPORT), SEXP_FALSE, SEXP_FALSE, 0, "peek-char", (sexp)"current-input-port", NULL),
 #endif
+_FN1OPTP(_I(SEXP_BOOLEAN), _I(SEXP_IPORT), "char-ready?", (sexp)"current-input-port", sexp_char_ready_p),
 _FN1OPTP(_I(SEXP_OBJECT), _I(SEXP_IPORT), "read", (sexp)"current-input-port", sexp_read_op),
 _FN2OPTP(SEXP_VOID,_I(SEXP_OBJECT), _I(SEXP_OPORT), "write", (sexp)"current-output-port", sexp_write_op),
 _FN1OPTP(SEXP_VOID, _I(SEXP_OPORT), "flush-output", (sexp)"current-output-port", sexp_flush_output_op),
diff --git a/sexp.c b/sexp.c
index 18a8d6d7..7ac2b9c3 100644
--- a/sexp.c
+++ b/sexp.c
@@ -1732,6 +1732,44 @@ void sexp_maybe_unblock_port (sexp ctx, sexp port) {
 }
 #endif
 
+#if SEXP_USE_GREEN_THREADS
+static int sexp_fileno_ready_p (int fd) {
+  struct pollfd pfd;
+  if (fd < 0) return -1;
+  pfd.fd = fd;
+  pfd.events = POLLIN;
+  return poll(&pfd, 1, 0) == 1;
+}
+
+static int sexp_stream_ready_p (FILE* in) {
+  int flags = fcntl(fileno(in), F_GETFL), res;
+  if (! (flags & O_NONBLOCK)) fcntl(fileno(in), F_SETFL, flags & O_NONBLOCK);
+  res = getc(in);
+  if (! (flags & O_NONBLOCK)) fcntl(fileno(in), F_SETFL, flags);
+  return (res == EOF) ? feof(in) : 1;
+}
+#endif
+
+sexp sexp_char_ready_p (sexp ctx, sexp self, sexp_sint_t n, sexp in) {
+  sexp_assert_type(ctx, sexp_iportp, SEXP_IPORT, in);
+  if (!sexp_port_openp(in))
+    return SEXP_FALSE;
+#if !SEXP_USE_STRING_STREAMS
+  if (sexp_port_buf(in))
+    if (sexp_port_offset(in) < sexp_port_size(in)
+        || (!sexp_filenop(sexp_port_fd(in)) && !sexp_port_stream(in)))
+      return SEXP_TRUE;
+#endif
+#if SEXP_USE_GREEN_THREADS     /* maybe not just when threads are enabled */
+  if (sexp_filenop(sexp_port_fd(in)))
+    return sexp_make_boolean(sexp_fileno_ready_p(sexp_port_fileno(in)));
+  else if (sexp_port_stream(in))
+    return sexp_make_boolean(sexp_stream_ready_p(sexp_port_stream(in)));
+#endif
+  /* for custom ports and unthreaded compiles we just return true for now */
+  return SEXP_TRUE;
+}
+
 #define NUMBUF_LEN 32
 
 static struct {const char* name; char ch;} sexp_char_names[] = {