diff --git a/libguile/backtrace.c b/libguile/backtrace.c
index d47375771..eb12df4db 100644
--- a/libguile/backtrace.c
+++ b/libguile/backtrace.c
@@ -99,7 +99,7 @@ scm_display_error_message (message, args, port)
   char *start;
   char *p;
   
-  if (SCM_IMP (message) || !SCM_STRINGP (message) || SCM_IMP (args)
+  if (SCM_IMP (message) || !SCM_ROSTRINGP (message) || SCM_IMP (args)
       || !scm_list_p (args))
     {
       scm_prin1 (message, port, 0);
@@ -107,7 +107,8 @@ scm_display_error_message (message, args, port)
       return;
     }
 
-  start = SCM_CHARS (message);
+  SCM_COERCE_SUBSTR (message);
+  start = SCM_ROCHARS (message);
   for (p = start; *p != '\0'; ++p)
     if (*p == '%')
       {
diff --git a/libguile/error.c b/libguile/error.c
index 910ad5c19..5d8a36247 100644
--- a/libguile/error.c
+++ b/libguile/error.c
@@ -84,7 +84,8 @@ scm_error (key, subr, message, args, rest)
   
   /* No return, but just in case: */
 
-  write (2, "unhandled system error", sizeof ("unhandled system error") - 1);
+  write (2, "unhandled system error\n",
+	 sizeof ("unhandled system error\n") - 1);
   exit (1);
 }
 
@@ -105,6 +106,8 @@ scm_error_scm (key, subr, message, args, rest)
 	      || (SCM_NIMP (message) && SCM_ROSTRINGP (message)),
 	      message, SCM_ARG3, s_error_scm);
 
+  SCM_COERCE_SUBSTR (message);
+
   scm_error (key,
 	     (SCM_FALSEP (subr)) ? NULL : SCM_ROCHARS (subr),
 	     (SCM_FALSEP (message)) ? NULL : SCM_ROCHARS (message),
diff --git a/libguile/filesys.c b/libguile/filesys.c
index 58011f609..750d5a2d3 100644
--- a/libguile/filesys.c
+++ b/libguile/filesys.c
@@ -139,10 +139,10 @@ scm_chown (path, owner, group)
   int val;
 
   SCM_ASSERT (SCM_NIMP (path) && SCM_ROSTRINGP (path), path, SCM_ARG1, s_chown);
-  if (SCM_SUBSTRP (path))
-    path = scm_makfromstr (SCM_ROCHARS (path), SCM_ROLENGTH (path), 0);
   SCM_ASSERT (SCM_INUMP (owner), owner, SCM_ARG2, s_chown);
   SCM_ASSERT (SCM_INUMP (group), group, SCM_ARG3, s_chown);
+
+  SCM_COERCE_SUBSTR (path);
   SCM_SYSCALL (val = chown (SCM_ROCHARS (path),
 			    SCM_INUM (owner), SCM_INUM (group)));
   if (val != 0)
@@ -161,8 +161,11 @@ scm_chmod (port_or_path, mode)
   int rv;
   SCM_ASSERT (SCM_INUMP (mode), mode, SCM_ARG2, s_chmod);
   SCM_ASSERT (SCM_NIMP (port_or_path), port_or_path, SCM_ARG1, s_chmod);
-  if (SCM_STRINGP (port_or_path))
-    SCM_SYSCALL (rv = chmod (SCM_CHARS (port_or_path), SCM_INUM (mode)));
+  if (SCM_ROSTRINGP (port_or_path))
+    {
+      SCM_COERCE_SUBSTR (port_or_path);
+      SCM_SYSCALL (rv = chmod (SCM_ROCHARS (port_or_path), SCM_INUM (mode)));
+    }
   else
     {
       SCM_ASSERT (SCM_OPFPORTP (port_or_path), port_or_path, SCM_ARG1, s_chmod);
@@ -438,22 +441,26 @@ scm_rename (oldname, newname)
      SCM newname;
 {
   int rv;
-  SCM_ASSERT (SCM_NIMP (oldname) && SCM_STRINGP (oldname), oldname, SCM_ARG1, s_rename);
-  SCM_ASSERT (SCM_NIMP (newname) && SCM_STRINGP (newname), newname, SCM_ARG2, s_rename);
+  SCM_ASSERT (SCM_NIMP (oldname) && SCM_ROSTRINGP (oldname), oldname, SCM_ARG1,
+	      s_rename);
+  SCM_ASSERT (SCM_NIMP (newname) && SCM_ROSTRINGP (newname), newname, SCM_ARG2,
+	      s_rename);
+  SCM_COERCE_SUBSTR (oldname);
+  SCM_COERCE_SUBSTR (newname);
 #ifdef HAVE_RENAME
-  SCM_SYSCALL (rv = rename (SCM_CHARS (oldname), SCM_CHARS (newname)));
+  SCM_SYSCALL (rv = rename (SCM_ROCHARS (oldname), SCM_ROCHARS (newname)));
   if (rv != 0)
     scm_syserror (s_rename);
   return SCM_UNSPECIFIED;
 #else
   SCM_DEFER_INTS;
-  SCM_SYSCALL (rv = link (SCM_CHARS (oldname), SCM_CHARS (newname)));
+  SCM_SYSCALL (rv = link (SCM_ROCHARS (oldname), SCM_ROCHARS (newname)));
   if (rv == 0)
     {
-      SCM_SYSCALL (rv = unlink (SCM_CHARS (oldname)));;
+      SCM_SYSCALL (rv = unlink (SCM_ROCHARS (oldname)));;
       if (rv != 0)
 	/* unlink failed.  remove new name */
-	SCM_SYSCALL (unlink (SCM_CHARS (newname))); 
+	SCM_SYSCALL (unlink (SCM_ROCHARS (newname))); 
     }
   SCM_ALLOW_INTS;
   if (rv != 0)
@@ -470,8 +477,9 @@ scm_delete_file (str)
      SCM str;
 {
   int ans;
-  SCM_ASSERT (SCM_NIMP (str) && SCM_STRINGP (str), str, SCM_ARG1, s_delete_file);
-  SCM_SYSCALL (ans = unlink (SCM_CHARS (str)));
+  SCM_ASSERT (SCM_NIMP (str) && SCM_ROSTRINGP (str), str, SCM_ARG1, s_delete_file);
+  SCM_COERCE_SUBSTR (str);
+  SCM_SYSCALL (ans = unlink (SCM_ROCHARS (str)));
   if (ans != 0)
     scm_syserror (s_delete_file);
   return SCM_UNSPECIFIED;
@@ -488,17 +496,19 @@ scm_mkdir (path, mode)
 #ifdef HAVE_MKDIR
   int rv;
   mode_t mask;
-  SCM_ASSERT (SCM_NIMP (path) && SCM_STRINGP (path), path, SCM_ARG1, s_mkdir);
+  SCM_ASSERT (SCM_NIMP (path) && SCM_ROSTRINGP (path), path, SCM_ARG1,
+	      s_mkdir);
+  SCM_COERCE_SUBSTR (path);
   if (SCM_UNBNDP (mode))
     {
       mask = umask (0);
       umask (mask);
-      SCM_SYSCALL (rv = mkdir (SCM_CHARS (path), 0777 ^ mask));
+      SCM_SYSCALL (rv = mkdir (SCM_ROCHARS (path), 0777 ^ mask));
     }
   else
     {
       SCM_ASSERT (SCM_INUMP (mode), mode, SCM_ARG2, s_mkdir);
-      SCM_SYSCALL (rv = mkdir (SCM_CHARS (path), SCM_INUM (mode)));
+      SCM_SYSCALL (rv = mkdir (SCM_ROCHARS (path), SCM_INUM (mode)));
     }
   if (rv != 0)
     scm_syserror (s_mkdir);
@@ -520,8 +530,10 @@ scm_rmdir (path)
 #ifdef HAVE_RMDIR
   int val;
 
-  SCM_ASSERT (SCM_NIMP (path) && SCM_STRINGP (path), path, SCM_ARG1, s_rmdir);
-  SCM_SYSCALL (val = rmdir (SCM_CHARS (path)));
+  SCM_ASSERT (SCM_NIMP (path) && SCM_ROSTRINGP (path), path, SCM_ARG1,
+	      s_rmdir);
+  SCM_COERCE_SUBSTR (path);
+  SCM_SYSCALL (val = rmdir (SCM_ROCHARS (path)));
   if (val != 0)
     scm_syserror (s_rmdir);
   return SCM_UNSPECIFIED;
@@ -546,10 +558,12 @@ scm_opendir (dirname)
 {
   DIR *ds;
   SCM dir;
-  SCM_ASSERT (SCM_NIMP (dirname) && SCM_STRINGP (dirname), dirname, SCM_ARG1, s_opendir);
+  SCM_ASSERT (SCM_NIMP (dirname) && SCM_ROSTRINGP (dirname), dirname, SCM_ARG1,
+	      s_opendir);
+  SCM_COERCE_SUBSTR (dirname);
   SCM_NEWCELL (dir);
   SCM_DEFER_INTS;
-  SCM_SYSCALL (ds = opendir (SCM_CHARS (dirname)));
+  SCM_SYSCALL (ds = opendir (SCM_ROCHARS (dirname)));
   if (ds == NULL)
     scm_syserror (s_opendir);
   SCM_SETCAR (dir, scm_tc16_dir | SCM_OPN);
@@ -657,8 +671,9 @@ scm_chdir (str)
 {
   int ans;
 
-  SCM_ASSERT (SCM_NIMP (str) && SCM_STRINGP (str), str, SCM_ARG1, s_chdir);
-  SCM_SYSCALL (ans = chdir (SCM_CHARS (str)));
+  SCM_ASSERT (SCM_NIMP (str) && SCM_ROSTRINGP (str), str, SCM_ARG1, s_chdir);
+  SCM_COERCE_SUBSTR (str);
+  SCM_SYSCALL (ans = chdir (SCM_ROCHARS (str)));
   if (ans != 0)
     scm_syserror (s_chdir);
   return SCM_UNSPECIFIED;
@@ -965,9 +980,13 @@ scm_symlink(oldpath, newpath)
 #ifdef HAVE_SYMLINK
   int val;
 
-  SCM_ASSERT(SCM_NIMP(oldpath) && SCM_STRINGP(oldpath), oldpath, SCM_ARG1, s_symlink);
-  SCM_ASSERT(SCM_NIMP(newpath) && SCM_STRINGP(newpath), newpath, SCM_ARG2, s_symlink);
-  SCM_SYSCALL (val = symlink(SCM_CHARS(oldpath), SCM_CHARS(newpath)));
+  SCM_ASSERT (SCM_NIMP (oldpath) && SCM_ROSTRINGP (oldpath), oldpath, SCM_ARG1,
+	      s_symlink);
+  SCM_ASSERT (SCM_NIMP (newpath) && SCM_ROSTRINGP (newpath), newpath, SCM_ARG2,
+	      s_symlink);
+  SCM_COERCE_SUBSTR (oldpath);
+  SCM_COERCE_SUBSTR (newpath);
+  SCM_SYSCALL (val = symlink(SCM_ROCHARS(oldpath), SCM_ROCHARS(newpath)));
   if (val != 0)
     scm_syserror (s_symlink);
   return SCM_UNSPECIFIED;
@@ -990,10 +1009,12 @@ scm_readlink(path)
   scm_sizet size = 100;
   char *buf;
   SCM result;
-  SCM_ASSERT (SCM_NIMP (path) && SCM_STRINGP (path),  path, (char *) SCM_ARG1, s_readlink);
+  SCM_ASSERT (SCM_NIMP (path) && SCM_ROSTRINGP (path), path, (char *) SCM_ARG1,
+	      s_readlink);
+  SCM_COERCE_SUBSTR (path);
   SCM_DEFER_INTS;
   buf = scm_must_malloc (size, s_readlink);
-  while ((rv = readlink (SCM_CHARS (path), buf, (scm_sizet) size)) == size)
+  while ((rv = readlink (SCM_ROCHARS (path), buf, (scm_sizet) size)) == size)
     {
       scm_must_free (buf);
       size *= 2;
@@ -1023,8 +1044,10 @@ scm_lstat(str)
   int rv;
   struct stat stat_temp;
 
-  SCM_ASSERT(SCM_NIMP(str) && SCM_STRINGP(str), str, (char *)SCM_ARG1, s_lstat);
-  SCM_SYSCALL(rv = lstat(SCM_CHARS(str), &stat_temp));
+  SCM_ASSERT (SCM_NIMP (str) && SCM_ROSTRINGP (str), str, (char *) SCM_ARG1,
+	      s_lstat);
+  SCM_COERCE_SUBSTR (str);
+  SCM_SYSCALL(rv = lstat(SCM_ROCHARS(str), &stat_temp));
   if (rv != 0)
     {
       int en = errno;
diff --git a/libguile/ioext.c b/libguile/ioext.c
index 255393a7d..a18654097 100644
--- a/libguile/ioext.c
+++ b/libguile/ioext.c
@@ -206,6 +206,9 @@ scm_freopen (filename, modes, port)
 	      SCM_ARG1, s_freopen);
   SCM_ASSERT (SCM_NIMP (modes) && SCM_ROSTRINGP (modes), modes, SCM_ARG2,
 	      s_freopen);
+
+  SCM_COERCE_SUBSTR (filename);
+  SCM_COERCE_SUBSTR (modes);
   SCM_DEFER_INTS;
   SCM_ASSERT (SCM_NIMP (port) && SCM_FPORTP (port), port, SCM_ARG3, s_freopen);
   SCM_SYSCALL (f = freopen (SCM_ROCHARS (filename), SCM_ROCHARS (modes),
@@ -247,6 +250,8 @@ scm_duplicate_port (oldpt, modes)
 	      s_duplicate_port);
   SCM_ASSERT (SCM_NIMP (modes) && SCM_ROSTRINGP (modes), modes, SCM_ARG2,
 	      s_duplicate_port);
+
+  SCM_COERCE_SUBSTR (modes);
   SCM_NEWCELL (newpt);
   SCM_DEFER_INTS;
   oldfd = fileno ((FILE *)SCM_STREAM (oldpt));
@@ -346,6 +351,7 @@ scm_fdopen (fdes, modes)
   SCM_ASSERT (SCM_INUMP (fdes), fdes, SCM_ARG1, s_fdopen);
   SCM_ASSERT (SCM_NIMP (modes) && SCM_ROSTRINGP (modes), modes, SCM_ARG2,
 	      s_fdopen);
+  SCM_COERCE_SUBSTR (modes);
   SCM_NEWCELL (port);
   SCM_DEFER_INTS;
   f = fdopen (SCM_INUM (fdes), SCM_ROCHARS (modes));
diff --git a/libguile/net_db.c b/libguile/net_db.c
index bb73295fd..c89a1f1ee 100644
--- a/libguile/net_db.c
+++ b/libguile/net_db.c
@@ -174,6 +174,7 @@ scm_gethost (name)
     }
   else if (SCM_NIMP (name) && SCM_ROSTRINGP (name))
     {
+      SCM_COERCE_SUBSTR (name);
       SCM_DEFER_INTS;
       entry = gethostbyname (SCM_ROCHARS (name));
     }
@@ -225,6 +226,7 @@ scm_getnet (name)
     }
   else if (SCM_NIMP (name) && SCM_ROSTRINGP (name))
     {
+      SCM_COERCE_SUBSTR (name);
       SCM_DEFER_INTS;
       entry = getnetbyname (SCM_ROCHARS (name));
     }
@@ -264,6 +266,7 @@ scm_getproto (name)
     }
   else if (SCM_NIMP (name) && SCM_ROSTRINGP (name))
     {
+      SCM_COERCE_SUBSTR (name);
       SCM_DEFER_INTS;
       entry = getprotobyname (SCM_ROCHARS (name));
     }
@@ -321,8 +324,10 @@ scm_getserv (name, proto)
       return scm_return_entry (entry);
     }
   SCM_ASSERT (SCM_NIMP (proto) && SCM_ROSTRINGP (proto), proto, SCM_ARG2, s_getserv);
+  SCM_COERCE_SUBSTR (proto);
   if (SCM_NIMP (name) && SCM_ROSTRINGP (name))
     {
+      SCM_COERCE_SUBSTR (name);
       SCM_DEFER_INTS;
       entry = getservbyname (SCM_ROCHARS (name), SCM_ROCHARS (proto));
     }
diff --git a/libguile/ports.c b/libguile/ports.c
index 0126c2f25..6a474900c 100644
--- a/libguile/ports.c
+++ b/libguile/ports.c
@@ -815,9 +815,10 @@ SCM
 scm_sys_make_void_port (mode)
      SCM mode;
 {
-  SCM_ASSERT (SCM_NIMP (mode) && SCM_STRINGP (mode), mode,
+  SCM_ASSERT (SCM_NIMP (mode) && SCM_ROSTRINGP (mode), mode,
 	      SCM_ARG1, s_sys_make_void_port);
 
+  SCM_COERCE_SUBSTR (mode);
   return scm_void_port (SCM_ROCHARS (mode));
 }
 
diff --git a/libguile/posix.c b/libguile/posix.c
index b511179c1..f0edefa6a 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -352,6 +352,7 @@ scm_getgrgid (name)
     {
       SCM_ASSERT (SCM_NIMP (name) && SCM_ROSTRINGP (name), name, SCM_ARG1,
 		  s_getgrgid);
+      SCM_COERCE_SUBSTR (name);
       SCM_SYSCALL (entry = getgrnam (SCM_ROCHARS (name)));
     }
   if (!entry)
@@ -972,9 +973,10 @@ scm_utime (pathname, actime, modtime)
   int rv;
   struct utimbuf utm_tmp;
 
-  SCM_ASSERT (SCM_NIMP (pathname) && SCM_STRINGP (pathname), pathname,
+  SCM_ASSERT (SCM_NIMP (pathname) && SCM_ROSTRINGP (pathname), pathname,
 	      SCM_ARG1, s_utime);
 
+  SCM_COERCE_SUBSTR (pathname);
   if (SCM_UNBNDP (actime))
     SCM_SYSCALL (time (&utm_tmp.actime));
   else
@@ -985,7 +987,7 @@ scm_utime (pathname, actime, modtime)
   else
     utm_tmp.modtime = scm_num2ulong (modtime, (char *) SCM_ARG3, s_utime);
 
-  SCM_SYSCALL (rv = utime (SCM_CHARS (pathname), &utm_tmp));
+  SCM_SYSCALL (rv = utime (SCM_ROCHARS (pathname), &utm_tmp));
   if (rv != 0)
     scm_syserror (s_utime);
   return SCM_UNSPECIFIED;
@@ -1026,12 +1028,13 @@ scm_putenv (str)
   int rv;
   char *ptr;
 
-  SCM_ASSERT (SCM_NIMP (str) && SCM_STRINGP (str), str, SCM_ARG1, s_putenv);
+  SCM_ASSERT (SCM_NIMP (str) && SCM_ROSTRINGP (str), str, SCM_ARG1, s_putenv);
   /* must make a new copy to be left in the environment, safe from gc.  */
   ptr = malloc (SCM_LENGTH (str) + 1);
   if (ptr == NULL)
     scm_memory_error (s_putenv);
-  strcpy (ptr, SCM_CHARS (str));
+  strncpy (ptr, SCM_ROCHARS (str), SCM_LENGTH (str));
+  ptr[SCM_LENGTH(str)] = 0;
   rv = putenv (ptr);
   if (rv < 0)
     scm_syserror (s_putenv);
@@ -1056,9 +1059,10 @@ scm_setlocale (category, locale)
     }
   else
     {
-      SCM_ASSERT (SCM_NIMP (locale) && SCM_STRINGP (locale), locale,
+      SCM_ASSERT (SCM_NIMP (locale) && SCM_ROSTRINGP (locale), locale,
 		  SCM_ARG2, s_setlocale);
-      clocale = SCM_CHARS (locale);
+      SCM_COERCE_SUBSTR (locale);
+      clocale = SCM_ROCHARS (locale);
     }
 
   rv = setlocale (SCM_INUM (category), clocale);
@@ -1090,6 +1094,7 @@ scm_mknod(path, type, perms, dev)
   SCM_ASSERT (SCM_NIMP(type) && SCM_SYMBOLP (type), type, SCM_ARG2, s_mknod);
   SCM_ASSERT (SCM_INUMP (perms), perms, SCM_ARG3, s_mknod);
   SCM_ASSERT (SCM_INUMP(dev), dev, SCM_ARG4, s_mknod);
+  SCM_COERCE_SUBSTR (path);
 
   p = SCM_CHARS (type);
   if (strcmp (p, "regular") == 0)
diff --git a/libguile/stime.c b/libguile/stime.c
index 47e8cae03..897b08ac8 100644
--- a/libguile/stime.c
+++ b/libguile/stime.c
@@ -245,14 +245,15 @@ setzone (SCM zone, int pos, char *subr)
       char *buf;
 
       /* if zone was supplied, set the environment variable TZ temporarily.  */
-      SCM_ASSERT (SCM_NIMP (zone) && SCM_STRINGP (zone), zone, pos, subr);
+      SCM_ASSERT (SCM_NIMP (zone) && SCM_ROSTRINGP (zone), zone, pos, subr);
+      SCM_COERCE_SUBSTR (zone);
       buf = malloc (SCM_LENGTH (zone) + 4);
       if (buf == 0)
 	scm_memory_error (subr);
       oldtz = getenv ("TZ");
       if (oldtz != NULL)
 	oldtz = oldtz - 3;
-      sprintf (buf, "TZ=%s", SCM_CHARS (zone));
+      sprintf (buf, "TZ=%s", SCM_ROCHARS (zone));
       if (putenv (buf) < 0)
 	scm_syserror (subr);
       tzset();
@@ -474,10 +475,11 @@ scm_strftime (format, stime)
   char *fmt;
   int len;
 
-  SCM_ASSERT (SCM_NIMP (format) && SCM_STRINGP (format), format, SCM_ARG1,
+  SCM_ASSERT (SCM_NIMP (format) && SCM_ROSTRINGP (format), format, SCM_ARG1,
 	      s_strftime);
   bdtime2c (stime, &t, SCM_ARG2, s_strftime);
 
+  SCM_COERCE_SUBSTR (format);
   fmt = SCM_ROCHARS (format);
   len = SCM_ROLENGTH (format);
 
@@ -507,6 +509,8 @@ scm_strptime (format, string)
   SCM_ASSERT (SCM_NIMP (string) && SCM_ROSTRINGP (string), string, SCM_ARG2,
 	      s_strptime);
 
+  SCM_COERCE_SUBSTR (format);
+  SCM_COERCE_SUBSTR (string);
   fmt = SCM_ROCHARS (format);
   str = SCM_ROCHARS (string);
 
diff --git a/libguile/symbols.h b/libguile/symbols.h
index d4808dc8b..ced3dda10 100644
--- a/libguile/symbols.h
+++ b/libguile/symbols.h
@@ -100,6 +100,9 @@ extern int scm_symhash_dim;
 #define SCM_SUBSTR_STR(x) (SCM_CDDR (x))
 #define SCM_SUBSTR_OFFSET(x) (SCM_CADR (x))
 
+#define SCM_COERCE_SUBSTR(x) { if (SCM_SUBSTRP (x)) \
+				 x = scm_makfromstr (SCM_ROCHARS (x), \
+						     SCM_ROLENGTH (x), 0); }
 
 
 
diff --git a/libguile/vports.c b/libguile/vports.c
index 89e398e98..b737455af 100644
--- a/libguile/vports.c
+++ b/libguile/vports.c
@@ -180,11 +180,12 @@ scm_make_soft_port (pv, modes)
   struct scm_port_table * pt;
   SCM z;
   SCM_ASSERT (SCM_NIMP (pv) && SCM_VECTORP (pv) && 5 == SCM_LENGTH (pv), pv, SCM_ARG1, s_make_soft_port);
-  SCM_ASSERT (SCM_NIMP (modes) && SCM_STRINGP (modes), modes, SCM_ARG2, s_make_soft_port);
+  SCM_ASSERT (SCM_NIMP (modes) && SCM_ROSTRINGP (modes), modes, SCM_ARG2, s_make_soft_port);
+  SCM_COERCE_SUBSTR (modes);
   SCM_NEWCELL (z);
   SCM_DEFER_INTS;
   pt = scm_add_to_port_table (z);
-  SCM_SETCAR (z, scm_tc16_sfport | scm_mode_bits (SCM_CHARS (modes)));
+  SCM_SETCAR (z, scm_tc16_sfport | scm_mode_bits (SCM_ROCHARS (modes)));
   SCM_SETPTAB_ENTRY (z, pt);
   SCM_SETSTREAM (z, pv);
   SCM_ALLOW_INTS;