diff --git a/lib/chibi/io/port.c b/lib/chibi/io/port.c
index 049f1ec6..4f546053 100644
--- a/lib/chibi/io/port.c
+++ b/lib/chibi/io/port.c
@@ -339,20 +339,31 @@ sexp sexp_read_u8 (sexp ctx, sexp self, sexp in) {
   sexp_assert_type(ctx, sexp_iportp, SEXP_IPORT, in);
   if (!sexp_port_binaryp(in))
     return sexp_xtype_exception(ctx, self, "not a binary port", in);
-  sexp_check_block_port(ctx, in, 0);
+#if SEXP_USE_GREEN_THREADS
+  errno = 0;
+#endif
   c = sexp_read_char(ctx, in);
-  return c == EOF ? SEXP_EOF : sexp_make_fixnum(c);
+  if (c == EOF) {
+#if SEXP_USE_GREEN_THREADS
+    if ((sexp_port_stream(in) ? ferror(sexp_port_stream(in)) : 1)
+        && (errno == EAGAIN)
+        && sexp_applicablep(sexp_global(ctx, SEXP_G_THREADS_BLOCKER))) {
+      if (sexp_port_stream(in))
+        clearerr(sexp_port_stream(in));
+      sexp_apply1(ctx, sexp_global(ctx, SEXP_G_THREADS_BLOCKER), in);
+      return sexp_global(ctx, SEXP_G_IO_BLOCK_ERROR);
+    }
+#endif
+    return SEXP_EOF;
+  }
+  if (c == '\n') sexp_port_line(in)++;
+  else if (c < 0) c += 128;
+  return sexp_make_fixnum(c);
 }
 
 sexp sexp_peek_u8 (sexp ctx, sexp self, sexp in) {
-  int c;
-  sexp_assert_type(ctx, sexp_iportp, SEXP_IPORT, in);
-  if (!sexp_port_binaryp(in))
-    return sexp_xtype_exception(ctx, self, "not a binary port", in);
-  sexp_check_block_port(ctx, in, 0);
-  c = sexp_read_char(ctx, in);
-  if (c == EOF)
-    return SEXP_EOF;
-  sexp_push_char(ctx, c, in);
-  return sexp_make_fixnum(c);
+  sexp res = sexp_read_u8(ctx, self, in);
+  if (sexp_charp(res))
+    sexp_push_char(ctx, sexp_unbox_character(res), in);
+  return res;
 }
diff --git a/sexp.c b/sexp.c
index 2fcc727f..d3df8449 100644
--- a/sexp.c
+++ b/sexp.c
@@ -1341,7 +1341,10 @@ sexp sexp_open_input_file_descriptor (sexp ctx, sexp self, sexp_sint_t n, sexp f
   in = fdopen(sexp_fileno_fd(fileno), "r");
   if (!in) return sexp_user_exception(ctx, SEXP_FALSE, "couldn't open fileno", fileno);
   res = sexp_make_input_port(ctx, in, SEXP_FALSE);
-  if (!sexp_exceptionp(res)) sexp_port_shutdownp(res) = sexp_truep(shutdownp);
+  if (!sexp_exceptionp(res)) {
+    sexp_port_binaryp(res) = 1;
+    sexp_port_shutdownp(res) = sexp_truep(shutdownp);
+  }
   return res;
 }
 
@@ -1536,6 +1539,7 @@ sexp sexp_open_input_file_descriptor (sexp ctx, sexp self, sexp_sint_t n, sexp f
   if (!sexp_exceptionp(res)) {
     sexp_port_fd(res) = fileno;
     sexp_port_offset(res) = SEXP_PORT_BUFFER_SIZE;
+    sexp_port_binaryp(res) = 1;
     sexp_port_shutdownp(res) = sexp_truep(shutdownp);
   }
   sexp_gc_release2(ctx);
@@ -1649,15 +1653,18 @@ sexp sexp_set_port_fold_case (sexp ctx, sexp self, sexp_sint_t n, sexp in, sexp
 int sexp_maybe_block_port (sexp ctx, sexp in, int forcep) {
   sexp f;
   int c;
-  if (sexp_port_stream(in) && sexp_port_fileno(in) >= 0) {
+  if ((sexp_port_stream(in) || sexp_filenop(sexp_port_fd(in)))
+      && sexp_port_fileno(in) >= 0) {
     if (sexp_port_flags(in) == SEXP_PORT_UNKNOWN_FLAGS)
       sexp_port_flags(in) = fcntl(sexp_port_fileno(in), F_GETFL);
     if (sexp_port_flags(in) & O_NONBLOCK) {
       if (!forcep
           && (((c = sexp_read_char(ctx, in)) == EOF)
               && sexp_port_stream(in)
-              && ferror(sexp_port_stream(in)) && (errno == EAGAIN))) {
-        clearerr(sexp_port_stream(in));
+              && (sexp_port_stream(in) ? ferror(sexp_port_stream(in)) : 1)
+              && (errno == EAGAIN))) {
+        if (sexp_port_stream(in))
+          clearerr(sexp_port_stream(in));
         f = sexp_global(ctx, SEXP_G_THREADS_BLOCKER);
         if (sexp_opcodep(f)) {
           ((sexp_proc2)sexp_opcode_func(f))(ctx, f, 1, in);