diff --git a/libguile/filesys.c b/libguile/filesys.c
index 7c4819f41..371d03aaf 100644
--- a/libguile/filesys.c
+++ b/libguile/filesys.c
@@ -28,6 +28,23 @@
 #  include <config.h>
 #endif
 
+/* AIX requires this to be the first thing in the file.  The #pragma
+   directive is indented so pre-ANSI compilers will ignore it, rather
+   than choke on it.  */
+#ifndef __GNUC__
+# if HAVE_ALLOCA_H
+#  include <alloca.h>
+# else
+#  ifdef _AIX
+#   pragma alloca
+#  else
+#   ifndef alloca /* predefined by HP cc +Olibcalls */
+char *alloca ();
+#   endif
+#  endif
+# endif
+#endif
+
 #include <stdio.h>
 #include <errno.h>
 
@@ -35,6 +52,7 @@
 #include "libguile/smob.h"
 #include "libguile/feature.h"
 #include "libguile/fports.h"
+#include "libguile/private-gc.h"  /* for SCM_MAX */
 #include "libguile/iselect.h"
 #include "libguile/strings.h"
 #include "libguile/vectors.h"
@@ -92,6 +110,7 @@
 #if defined (__MINGW32__) || defined (_MSC_VER) || defined (__BORLANDC__)
 # include "win32-dirent.h"
 # define NAMLEN(dirent) strlen((dirent)->d_name)
+/* The following bits are per AC_HEADER_DIRENT doco in the autoconf manual */
 #elif HAVE_DIRENT_H
 # include <dirent.h>
 # define NAMLEN(dirent) strlen((dirent)->d_name)
@@ -178,6 +197,13 @@
 # define fsync(fd) _commit (fd)
 # define fchmod(fd, mode) (-1)
 #endif /* __MINGW32__ */
+
+/* This definition is for Solaris 10, it's probably not right elsewhere, but
+   that's ok, it shouldn't be used elsewhere.  */
+#if ! HAVE_DIRFD
+#define dirfd(dirstream) (dirstream->dd_fd)
+#endif
+
 
 
 /* Two helper macros for an often used pattern */
@@ -831,8 +857,9 @@ SCM_DEFINE (scm_opendir, "opendir", 1, 0, 0,
 
 /* FIXME: The glibc manual has a portability note that readdir_r may not
    null-terminate its return string.  The circumstances outlined for this
-   are not clear, nor is it clear what should be done about it.  Lets worry
-   about this if/when someone can figure it out.  */
+   are not clear, nor is it clear what should be done about it.  Lets use
+   NAMLEN and worry about what else should be done if/when someone can
+   figure it out.  */
 
 SCM_DEFINE (scm_readdir, "readdir", 1, 0, 0, 
             (SCM port),
@@ -847,29 +874,67 @@ SCM_DEFINE (scm_readdir, "readdir", 1, 0, 0,
   if (!SCM_DIR_OPEN_P (port))
     SCM_MISC_ERROR ("Directory ~S is not open.", scm_list_1 (port));
 
-  errno = 0;
-  {
 #if HAVE_READDIR_R
-    /* On Solaris 2.7, struct dirent only contains "char d_name[1]" and one is
-       expected to provide a buffer of "sizeof(struct dirent) + NAME_MAX"
-       bytes.  The glibc 2.3.2 manual notes this sort of thing too, and
-       advises "offsetof(struct dirent,d_name) + NAME_MAX + 1".  Either should
-       suffice, we give both to be certain.  */
-    union {
-      struct dirent ent;
-      char pad1 [sizeof(struct dirent) + NAME_MAX];
-      char pad2 [offsetof (struct dirent, d_name) + NAME_MAX + 1];
-    } u;
-    SCM_SYSCALL (readdir_r ((DIR *) SCM_CELL_WORD_1 (port), &u.ent, &rdent));
+  /* As noted in the glibc manual, on various systems (such as Solaris) the
+     d_name[] field is only 1 char and you're expected to size the dirent
+     buffer for readdir_r based on NAME_MAX.  The SCM_MAX expressions below
+     effectively give either sizeof(d_name) or NAME_MAX+1, whichever is
+     bigger.
+
+     On solaris 10 there's no NAME_MAX constant, it's necessary to use
+     pathconf().  We prefer NAME_MAX though, since it should be a constant
+     and will therefore save a system call.  We also prefer it since dirfd()
+     is not available everywhere.
+
+     An alternative to dirfd() would be to open() the directory and then use
+     fdopendir(), if the latter is available.  That'd let us hold the fd
+     somewhere in the smob, or just the dirent size calculated once.  */
+  {
+    struct dirent de; /* just for sizeof */
+    DIR    *ds = (DIR *) SCM_CELL_WORD_1 (port);
+    size_t namlen;
+#ifdef NAME_MAX
+    char   buf [SCM_MAX (sizeof (de),
+                         sizeof (de) - sizeof (de.d_name) + NAME_MAX + 1)];
 #else
-    SCM_SYSCALL (rdent = readdir ((DIR *) SCM_CELL_WORD_1 (port)));
+    char   *buf;
+    long   name_max = fpathconf (dirfd (ds), _PC_NAME_MAX);
+    if (name_max == -1)
+      SCM_SYSERROR;
+    buf = alloca (SCM_MAX (sizeof (de),
+                           sizeof (de) - sizeof (de.d_name) + name_max + 1));
 #endif
+
+    errno = 0;
+    SCM_SYSCALL (readdir_r (ds, (struct dirent *) buf, &rdent));
     if (errno != 0)
       SCM_SYSERROR;
+    if (! rdent)
+      return SCM_EOF_VAL;
+
+    namlen = NAMLEN (rdent);
 
     return (rdent ? scm_from_locale_stringn (rdent->d_name, NAMLEN (rdent))
             : SCM_EOF_VAL);
   }
+#else
+  {
+    SCM ret;
+    scm_dynwind_begin (0);
+    scm_i_dynwind_pthread_mutex_lock (&scm_i_misc_mutex);
+
+    errno = 0;
+    SCM_SYSCALL (rdent = readdir ((DIR *) SCM_CELL_WORD_1 (port)));
+    if (errno != 0)
+      SCM_SYSERROR;
+
+    ret = (rdent ? scm_from_locale_stringn (rdent->d_name, NAMLEN (rdent))
+           : SCM_EOF_VAL);
+
+    scm_dynwind_end ();
+    return ret;
+  }
+#endif
 }
 #undef FUNC_NAME