diff --git a/src/main.c b/src/main.c
index 81bdba3..26c4a0b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,6 +1,6 @@
 /*
   mboxgrep - scan mailbox for messages matching a regular expression
-  Copyright (C) 2000 - 2004, 2006, 2023  Daniel Spiljar
+  Copyright (C) 2000 - 2004, 2006, 2023 - 2024  Daniel Spiljar
 
   Mboxgrep is free software; you can redistribute it and/or modify it 
   under the terms of the GNU General Public License as published by
@@ -117,7 +117,7 @@ main (int argc, char **argv)
       if (config.action == ACTION_DELETE)
         {
           tmpmbox_create (argv[optind]);
-          runtime.tmp_mbox = (mbox_t *) mbox_open (config.tmpfilename, "w");
+          runtime.tmp_mbox = (mbox_t *) mbox_open (config.tmpfilename, w);
         }
 
       config.boxname = xstrdup (argv[optind]);
diff --git a/src/mbox.c b/src/mbox.c
index 32b2bfc..ba119ed 100644
--- a/src/mbox.c
+++ b/src/mbox.c
@@ -50,7 +50,7 @@
 #endif /* HAVE_LIBDMALLOC */
 
 mbox_t *
-mbox_open (const char *path, const char *mode)
+mbox_open (const char *path, const mbox_mode_t mbox_mode)
 {
   mbox_t *mp;
   static int fd;
@@ -66,17 +66,11 @@ mbox_open (const char *path, const char *mode)
     mp->fp = stdin;
   else
     {
-      if (mode[0] == 'r')
-        fd = m_open (path, O_RDONLY, 0);
-      else if (mode[0] == 'w')
+      if (mbox_mode == w)
         fd = m_open (path, (O_WRONLY | O_CREAT | O_APPEND),
                      (S_IWUSR | S_IRUSR));
       else
-        {
-          fprintf (stderr, "%s: mbox.c: Unknown mode %c.  You shouldn't "
-                   "get this error...", APPNAME, mode[0]);
-          exit (2);
-        }
+        fd = m_open (path, O_RDONLY, 0);
 
       if (fd == -1)
         {
@@ -90,9 +84,9 @@ mbox_open (const char *path, const char *mode)
         }
 
       if (config.lock > LOCK_NONE)
-        mbox_lock (fd, path, mode);
+        mbox_lock (fd, path, mbox_mode);
 
-      if (mode[0] == 'r')
+      if (mbox_mode == r)
         {
           if (config.format == FORMAT_MBOX)
             mp->fp = (FILE *) m_fdopen (fd, "r");
@@ -105,7 +99,7 @@ mbox_open (const char *path, const char *mode)
             mp->fp = (BZFILE *) BZ2_bzdopen (fd, "rb");
 #endif /* HAVE_LIBBZ2 */
         }
-      else if (mode[0] == 'w')
+      else if (mbox_mode == w)
         {
           if (config.format == FORMAT_MBOX)
             mp->fp = (FILE *) m_fdopen (fd, "w");
@@ -134,7 +128,7 @@ mbox_open (const char *path, const char *mode)
 
   memset (buffer, 0, BUFSIZ);
 
-  if (mode[0] == 'r')
+  if (mbox_mode == r)
     {
       if (config.format == FORMAT_MBOX)
         fgets (buffer, BUFSIZ, mp->fp);
@@ -406,12 +400,12 @@ tmpfile_create (void)
 }
 
 void
-mbox_lock (int fd, const char *path, const char *mode)
+mbox_lock (int fd, const char *path, const mbox_mode_t mbox_mode)
 {
 #ifdef HAVE_FLOCK
   int op;
 
-  if (mode[0] == 'r')
+  if (mbox_mode == r)
     op = LOCK_SH;
   else
     op = LOCK_EX;
diff --git a/src/mbox.h b/src/mbox.h
index e739180..4776383 100644
--- a/src/mbox.h
+++ b/src/mbox.h
@@ -19,9 +19,7 @@
 
 #ifndef MBOX_H
 #  define MBOX_H 1
-
 #  include <config.h>
-
 #  include "message.h"
 
 typedef struct
@@ -31,8 +29,14 @@ typedef struct
   char *postmark_cache;
 } mbox_t;
 
+typedef enum
+{
+  r,
+  w,
+} mbox_mode_t;
 
-mbox_t *mbox_open (const char *path, const char *mode);
+
+mbox_t *mbox_open (const char *path, const mbox_mode_t mbox_mode);
 void tmpmbox_create (const char *path);
 void tmpfile_name (const char *path);
 void tmpfile_mod_own (const int fd, const char *path);
@@ -40,6 +44,6 @@ int tmpfile_create (void);
 void mbox_close (mbox_t * mbp);
 message_t *mbox_read_message (mbox_t * mp);
 void mbox_write_message (message_t * m, mbox_t * mbox);
-void mbox_lock (int fd, const char *path, const char *mode);
+void mbox_lock (int fd, const char *path, const mbox_mode_t mbox_mode);
 
 #endif /* MBOX_H */
diff --git a/src/scan.c b/src/scan.c
index 85f19f9..69ff4fd 100644
--- a/src/scan.c
+++ b/src/scan.c
@@ -1,6 +1,6 @@
 /*
    mboxgrep - scan mailbox for messages matching a regular expression
-   Copyright (C) 2000 - 2004, 2006, 2023  Daniel Spiljar
+   Copyright (C) 2000 - 2004, 2006, 2023 - 2024  Daniel Spiljar
    
    Mboxgrep is free software; you can redistribute it and/or modify it 
    under the terms of the GNU General Public License as published by
@@ -107,7 +107,7 @@ scan_mailbox (char path[])
   if ((config.format == FORMAT_MBOX) || (config.format == FORMAT_ZMBOX)
       || (config.format == FORMAT_BZ2MBOX))
     {
-      mbox = (mbox_t *) mbox_open (path, "r");
+      mbox = (mbox_t *) mbox_open (path, r);
       if (mbox == NULL)
         return;
     }
@@ -179,7 +179,7 @@ scan_mailbox (char path[])
               else if ((config.format == FORMAT_MBOX) || (config.format == FORMAT_ZMBOX)
                        || (config.format == FORMAT_BZ2MBOX))
                 {
-                  out = mbox_open (config.outboxname, "w");
+                  out = mbox_open (config.outboxname, w);
                   /* fprintf (out->fp, "%s\n%s", msg->headers, msg->body); */
                   mbox_write_message (msg, out);
                   mbox_close (out);